F, M MO N 8 ' AS T R O N O M Y 



ELEMENTARY 



ASTEONOMY: 



USE OF PUBLIC SCHOOLS, 



AND PRIVATE FAMILIES. 



By Prof. WM. EMMONS, Elba, N.Y. 

Late Lecturer on Astronomy, in Cary Collegiate Seminary ; Author of a 

Series of Astronomical Maps. 



QB 

46 



SECOND REVISED EDITION. 



ROCHESTER: 

FA..LS. BOOK & JOB PRINTER, OVER 21 BUFFALO STREET. 

1866. 



t LI BRARY OF CONGRES S, t 

t -**# t 



| UNITED STATES OF AMERICA,} 



£MMONS' ASTRONOMY. 



ELEMENTARY 



ASTEONOMY 



FOR THE 



USE. OF PUBLIC SCHOOLS, 



AND PRIVATE FAMILIES, 



By Prof. WM, EMMONS, Elba, N.Yi 

Late Lecturer on Astronomy, in Cary Collegiate Seminary; Author of 

Series of Astronomical Maps. 



SECOND REVISED EDITION, 



-*-♦-#■ 






ROCHESTER: 

WMj S. FALLS, BOOK & JOB PRINTER, OVER 21 BUFFALO STREET, 
186& 



Entered according to Act of Congress, in the year 1835, 

BY WILLIAM EMMONS, 

In the Clerk's Office of the District Court of the United States 

for the Northern District of New York. 



£ 



6* 






PREFACE. 



It is due to the public, that a succinct statement be made of the 
reasons which have induced the author to introduce this new can- 
didate for favor and patronage. Works of great merit and worth, 
tsn the Science of Astronomy, abound; but they do not fully meet the 
wants of the learner in Elementary Astronomy. Most of them are 
mathematically abstruse, and are interspersed with such multitudes 
of separate diagrams, that the learner becomes confused, and fails 
to obtain a clear and comprehensive idea of the anatomy and 
structure of the Solar System. 

From a diagram of the earth in one place ; of the moon, in an- 
other ; of the planets, somewhere else ; of solar and lunar eclipses, 
m another ; detached portions of the orbits of planets, elsewhere ; 
and comets, &c. &c, in still another place — most young learners ob- 
tain as clear and well-defined conceptions of the grand and harmo- 
nious structure of the Solar System, as would a boy, of a clock or 
watch, who had never seen one in all the nice combinations of their 
parts, by simply seeing detached and intricate portions scattered 
around him. 

Several years since, the author published an Astronomical Chart 
or Diagram, in which the structure of the Solar System, is exhibited 
at one view. A prominent design of the present work, is to teach 
afcd illustrate Astronomy in connection with that Chart, 



II PREFACE. 

The author has been induced to undertake the preparation a/id' 
publication of this work, through the repeated and urgent solicita- 
tions of numerous teachers and other scientific gentlemen ; and 
from the flattering reception which his Chart has received from 
the public. 

It is with great pleasure that he acknowledges his indebtedness 
to numerous authors, from whose works valuable assistance has 
been obtained in the preparation of this treatise. Among the As- 
tronomical works consulted, may be named, Mattison's, Brockelby's f 
Robinson's, Mitchell's, and Dick's. 

Entire perfection is not claimed for this work ; but it is given to 
the public, in the confidence that its merits will receive that com- 
mendation to which it is entitled* 

WM, EMMONS. 

Elba, N. Y., April, 1866, 



ASTRONOMY, 



LESSON L 

Question. What is Astronomy ? 

Answer. Astronomy is the science which treats of the 
heavenly bodies, describes their appearances, determines 
their magnitudes, and discovers the laws which govern 
their motions. 

Q. What are the Divisions of Astronomy ? 

A. Astronomy is divided into Descriptive, Practical^ 
Physical and Nautical. 

Q. What is Descriptive Astronomy ? 

A. A description of the appearances and a statement 
of the facts of the heavenly bodies. 

Q. What is Practical Astronomy? 

A. It consists in computing the magnitudes, determin- 
ing the distances, recording observations, and making as- 
tronomical computations. 

Q. What is Physical Astronomy ? 

A. It Jls the investigation of the laws which govern the 
eelestial motions, and the explanation of the causes which 
bring about their known results. 

Q. What is Nautical Astronomy ? 

A. It is to determine positions on the earth, and sub- 
sequently the magnitude of the earth : and hence it is 



6 ELEMENTARY ASTRONOMY. 

apparent that Geography and Astronomy are intimately 
Mended together, and the one science cannot be fully un- 
derstood without the aid of the other. 

Q. Is the Science, of Astronomy of a recent or of an- 
cient date ? 

A. None of the sciences ean claim a more remote anti- 
quity than that of Astronomy. Job, 1,500 years before 
Christ, speaks of Arcturus, Orion and Pleiades, and the 
Chambers of the South ; constellations still known by the 
same names, 

Q. Who was the first regular Teacher of Astronomy? 

A. Thales, one of the seven wise men of Greece, w T ho 
flourished 600 years before Christ. 

Q. Who first taught that the Sun was placed in the 
eenter of the Planetary Orbits ? 

A. Pythagoras, 500 years before Christ. 

Q. What other great Astronomer next embraced and 
defended the same views? 

A. Nicholas Copernicus, a celebrated Prussian astron- 
omer, in A. D. 1510, revived the ancient theory of Pytha- 
goras, which places the sun in the center of the solar 
system, and sets all the planets in rapid motion around 
him, as the central and controling force. 

Q. What constitutes the Heavenly Bodies ? 

A. The sun, moons, planets, comets, and stars. # 

Q. Of what characteristics of the Heavenly Bodies, 
does Astronomy treat ? 

A. Their appearance, size, form, arrangement, distance, 
motions, physical constitution, and their influence on each 
other. 



ELEMENTARY ASTRONOMY, 7 

Q. Are all the Planets, Stars, Comets, &o., of the same 
size? 

A. They are not. The sun and stars are much larger 
than the planets and moons. 

Q. Are they all at the same distance from the Earth? 

A. No. The moon is only 240 thousands of miles from 
the earth, while the sun is 95 millions of miles, and the 
nearest fixed star is not less than 20 billions of miles dis- 
tant. 



LESSON II. 



Q. Have all the Heavenly Bodies an inherent splendor, 
so that they emit light of themselves ? 

A. No. Some of them are luminous, and some of them 
are opaque. 

Q. What do you mean by a Luminous Body ? 

A. A body which shines by its own native or inherent 
splendor — one whose light is in itself; as the sun and 
fixed stars. 

Q. What is an Opaque Body ? 

A. An opaque body is one that can shine only by re- 
flecting the light of a luminous bod}' ; as the planets, 
moons and comets, shine only by reflecting the light of 
the sun. 

Q. Why do the Moons, Planets and Comets, appear to 
us as Luminous Bodies, if they are not really such ? 

A. Because they reflect back to the earth the light of 
the sun. 

Q. What is the form of the Heavenly Bodies? 



8 ELEMENTARY ASTRONOMY. 

A. They are nearly round, like a globe or ball ; but 
they more exactly resemble an oblate spheroid. 

Q. What constitutes the Solar System ? 

A. The sun, planets, moons and comets. 

Q. Are the Sun, Moons, Planets and Comets, of the 
Solar System, quiescent bodies, or have they, or any of 
them, motions of any kind ? 

A. All the planets, moons and comets, are in rapid and 
perpetual motion around the sun, according to the laws of 
central forces and circular motion. 

Q. How are the bodies of the Solar System arranged? 

A. The sun is situated in the center of the system, with 
the planets and comets revolving around him at very un- 
equal distances. 

Q. What is the direction of the Planets around the Sun ? 

A, From west to east, or the direction the earth would 
move to reach the places indicated on the Chart, during 
the several months of the year. 

Q. What is the order in which the Planets are arranged 
in the Solar System ? 

A. The sun is in or near the center, and all the planets 
perform their revolutions around this central luminary, in 
the following order : 

1. The planet Mercury, at the distance from the sun's 
centre, of - - 37 millions of miles. 

2. Venus, - 69 " " 

3. The Earth, - 95 " 

4. Mars, - 145 " " 

5. The Asteroids, from 210 to 300 " " 

6. Jupiter, - 496 " " 



ELEMENTARY ASTRONOMY. 9 

7. Saturn, - 907 millions of miles. 

8. Uranus, - - - 1,824 " " 

9. Neptune, - - 2,850 " " 

Q. How many Planets are there in the Solar System ? 

A. Eighty -three is the number known at this time. 

Q. Are the Planets all of the same size ? 

A. No. Some of them are many hundreds of times 
larger than others. 

Q. How many large Planets are there? 

A. Eight ; viz. Mercury, Venus, the Earth, Mars, Jupi- 
ter, Saturn, "Uranus, and Neptune. 

Q. How many small Planets are there, and what are 
they called? 

A. Fifty-seven, called Asteroids. 



LESSON III. 



Q. Where is the place of the Asteroids in the Solar 
System, where they perform their Revolutions around the 
Sun? 

A. They all revolve between the orbits of Mars and 
Jupiter — a space of about 349 millions of miles. 

Q. How are the Planets Classified or Divided, with re- 
ference to their motion ? 

A. They are divided into two classes, primary and 
secondary. 

Q. What is a Primary Planet ? 

A. It is one which revolves around the sun only. 

Q. What is a Secondary Planet ? 
1* 



10 ELEMENTARY ASTRONOMY. 

A. A secondary planet is one that revolves around a 
primary planet, and accompanies it in its journey around 
the sun. 

Q, What are the Secondary Planets usually called ? 

A. They are called satellites or moons. 

QUESTIONS ON THE CHART. 

Q. How are the Planets shown on the Chart ? 

A. Around the sun at unequal distances, the planets 
are shown in their orbits. A number of them are seen 
attended with a retinue of moons ; and Saturn is shown 
with two broad rings and eight moons. 

Q. What is represented on the Chart by the large and 
small Circles and Circular Figures? 

A. The large circles represent the orbits or paths in 
which the planets move around the sun ; and the small 
circles represent the orbits or paths of the satellites or 
moons around their primaries ; and the circular figures in 
the large circles or orbits represent the planets ; while the 
small circular figures in the small circles or orbits repre- 
sent the moons of the planets. 

Q. What is shown by this from the Chart? 

A. That while the planets are revolving around the sun, 
the secondaries or moons are moving around their prima- 
ries, and keeping up with them in their long journeys 
around the great central luminary. 

Q. What are the Names of the Primary Planets, begin- 
ning at the Sun ? 

A. Mercury, Yenus, the Earth, Mars, fifty-seven small 
planets called Asteroids, Jupiter, Saturn, Uranus, and 
Neptune. 



E L E MENTAK Y A S T R N'OMY. 11 

Q. How many Secondary Planets or Moons are there 
in the Solar System ? 

A. It is not positively known that there are more than 
twenty. 

Q. Which of the Planets have Moons ? 

A. The Earth has one ; Jupiter, four ; Saturn, eight ; 
Uranus, six ; and Neptune, one. 

Q. How many Asteroids or Small Planets are shown 
on the Chart ? 

A. Four, viz. Ceres, Pallas, Juno, and Vesta, 



LESSON IV. 



Q. Have the Planets any other Revolutions than their 
journeys around the Sun? 

A. Several of them are known to have two revolutions — 
a rotation on their axis, in connection with their annual 
revolution around the sun. 

Q. What is meant by the Axis of a Planet ? 

A. The axis of a planet is a straight line, round which 
it turns. 

Q. What is produced by the Rotation of a Planet on its 
Axis? 

A. It has day and night, 

Q. What is the Path called, in which a Planet moves 
around the Sun ? 

A. It is called its orbit ; as the large circles on the Dia- 
gram or Chart, represent the paths or orbits in which the 
planets respectively revolve around the sun. 



12 ELEMENTARY ASTRONOMY. 

Q. What is the Earth's Orbit called ? 

A. It is called the ecliptic. 

Q. Why is it called the Ecliptic? 

A. Because, eclipses can only happen when the moon 
is in the plane of its orbit. 

Q. What is meant by the Plane of the Earth's Orbit? 

A. The smooth and level surface, stretching from one 
side of the orbit across to- the other side. 

Q. How many Revolutions have the Secondary Planets 
or Moons ? 

A. Three. 

Q. What are those Planets called whose orbits lie be- 
tween the Earth and Sun ? 

A. They are termed interior planets, because their or- 
bits lie within the earth's orbit. 

Q. What are all those Planets called whose, orbits are 
beyond or exterior to the Earth's Orbit ? 

A. They are called exterior planets, because they per- 
form their revolutions in orbits which lie beyond the 
earth's orbit. The position of all the planets > interior and 
exterior, will be readily seen by an inspection of the Chart. 
It will there be observed that Mercury and Venus are in- 
terior planets, since their orbits are within the earth's 
orbit; and that Mars, the Asteroids, Jupiter, Saturn, Ura- 
nus and Neptune, are exterior planets, because their orbits 
lie outside or beyond the earth's orbit. 



ELEMENTARY ASTRONOMY. 13 



LESSON V. 



Q. Has the Earth in all ages been regarded as a Plane- 
tary Body, and connected with the Solar System? 

A. It has not. 

Q. Why did the Ancients suppose it to be an Extended 
Plain ? 

A. They judged only from appearances, 

Q. Did they suppose the Earth had any Motion? 

A. They did not. 

Q. What did they suppose held up the Earth ? 

A. They had no settled and well defined views on this 
point. 

Q. In what direction did the Ancients suppose the Sun, 
Moon and Stars revolved?' 

A. They supposed that they revolved around the earth 
from east to west, every twenty-four hours. 

Q. What was this system called that supposed the 
Earth to be at rest in the center of the Universe, with all 
the Heavenly Bodies revolving around it? 

A. The Ptolemaic System, from Ptolomy, an Egyptian 
philosopher of the second century. 

Q. We daily see the Sun rise in the East and set in the 
West. Where does it go during the night ? 

A. It appears to pass round under the earth, The stars, 
too, seem to pass round like the sun, under the earth every 
twenty-four hours. 

Q. Is such really the case, or are these Motions only 
apparent ? 

A. They are not real, but are only apparent, and are 



14 ELEMENTARY ASTRONOMY. 

caused by the motion of the earth in the opposite direc- 
tion, or from west to east. 

Q. Do we see any Bodies that seem to rest on no foun- 
dations ? 

A. We see the sun and moon resting on nothing, and 
suspended in empty space. 

Q. Is it not, then, reasonable to suppose that the Earth 
may rest on nothing ? 

A. It is as reasonable as that other of the heavenly 
bodies should have no foundations. 

Q. If the Earth turns, and we are carried round with it, 
what will be the appearance of the Heavens ? 

A. They will appear to move round the earth in the 
opposite direction. 

Q. ,How swiftly does the Earth Moove on its Axis ? 

A. Over one thousand miles per hour. 

Q. How swiftly does the Earth Fly in its Orbit around 
the Sun ? 

A. About sixty-eight thousand miles per hour. 

Q. Does the Earth Move in a Straight Line ? 

A. No. It is drawn from a straight to a curve line, by 
the attraction of the sun. 

Q. Do any other Bodies Revolve around the Sun? 

A. All the planets, both primary and secondary, do, as 
is shown on the Chart. The primary planets revolve di- 
rectly around the sun as their center of motion, and the 
secondary planets or moons revolve around their primaries, 
and accompany them in their long journies around the 
sun. 



ELEMENTARY ASTRONOMY. 15 

LESSON VI. 

CENTRIPETAL AND CENTRIFUGAL f ORCES. 

Q. What is the name of that Force that draws all bodies 
toward each other, in proportion to the quantity of matter 
they contain, and inversely, as the square of the distances 
of the attracting body ? 

A. The attraction of gravity or gravitation. 

Q. Does this Force pervade the whole material Uni- 
verse ? 

A. It undoubtedly does ; and retains all the planets, 
satellites and comets of the solar system in their respec- 
tive places, and binds the unnumbered millions of globes 
that belong to the universe into one vast and harmonious 
system. 

Q. What is meant by Centripetal Force ? 

A. It is that attractive power or force which impels a 
body toward the center, round which it is revolving. 

Q. Is there any large body in the Solar System that 
exerts a Centripetal Force upon the Planets and the 
Comets ? 

A. The sun, from his stupendous mass of matter, exerts 
such a force upon all the primary planets ; that they are 
retained in their orbits, and none ever wander from its 
appropriate place from age to age. 

Q. What retains the Moon in its Orbit around the 
Earth ? 

A. The earth and all the primary planets exert such a 
centripetal force upon their secondaries or moons. 



16 ELEMENTARY ASTRONOMY, 

Q. Why are not the Primary Planets attracted to the 
body of the Sun, and the Secondary Planets attracted to 
their primaries? 

A. The centrifugal force they received when thrown 
from the hand of the Deity, impelling them to move off 
in straight hues, wh:ch is nicely adjusted to the centripetal 
force, and the combination of the two produces the curve 
line called a planetary orbit. 

Q. Do the Planets move in Perfect Circles ? 

A. They do not. Their orbits are illiptical, as is seen 
in the figures A, P, B, D, E, C, S, on the left at the top 
of the Chart. The longest diameter is A, B, and the 
shortest is P, D. C, is the center of the ellipse, and S 
and E, are the foci around which the ellipse is formed. 

Q. Is the Sun placed at the center of the Ellipse? 

A. It is not. It is at S, the lower foci of the ellipse ; 
and the distance from the center to either of the foci, 
which is equal, is called the eccentricity of the ellipse. 

Q. When are Circles said to be in the same Plane ? 

A. When their planes are in a straight line; as if a 
number of concentric rings, or rings of different sizes, lav 
one within another upon the smooth surface of a table. 

Q. Do the Orbits of all the Planets lie in the same 
Plane ? 

A. They do not. The orbit of Jupiter lies in the same 
plane as that of the earth; but the plane of all the rest 
rises above the ecliptic, or the plane of the earth's orbit; 
or one half of each rises above it, while the other half 
falls below it. * 



E L E M E XT A R Y A ST RO XO M V . 17 

Q. Do the Planets all pass around the Sun in the same 
-length of time ? 

A. They do not. They vary from 88 days to 164 years. 
The planets nearest the sun complete their revolutions in 
the shortest periods of time, and those most remote in 
longer periods. 

Q. Do all the Planets move with equal Velocities ? 

A. They do not. The nearest planet to the sun moves 
110 thousand miles per hour, while the most distant one 
known moves but 15 thousand miles per hour. 



LESSON TIL— The Sun. 



Q. What is the largest globe in the Solar System ? 

A. The Sun. 

Q. What is the Size of the Sun? 

A. It is about 880 thousand miles in diameter, and 
2,264 thousand miles in circumference. 

Q. Why does the Sun appear so small — only about the 
size of the Moon ? 

A. Because it is so far from the earth. 

Q. What farther can you say of the Sun ? 

A. It is the great source of light, heat and attraction, 
and retains the planets in their orbits. Were the sun 
placed where the earth is, he would fill the space within 
the orbit of the moon, and extend 200 thousand miles 
beyond in every direction. It would require 112 such 
globes as the earth, if laid side by side, to reach across 
his vast diameter. 



18 ELEMENTARY ASTRONOMY. 

Q. Is the Sun larger than the Earth ? 

A. He is more than one million and three hundred 
thousand times as large as the earth. 

Q. Are any of the Planets as large as the Sun ? 

A. They are not. The sun is 500 times larger than all 
the planets, satellites and comets m the system, taken 
together. 

Q. What is the Mass or Weight of the Sun? 

A. It is about V50 times that of all the planets. 

Q. AT hat is the Specific Gravity of the Sun? 
A. About 1J the weight of water. 

Q. What did Astronomers in the early ages suppose the 
Sun to be ! 

A. An immense ball of fire. 

Q. Has the Sun any Motion ? 

A. It has three motions, as follows: 1. It revolves on 
its axis in 25 J days. 2. Around the center of gravity of 
the solar system. 3. Around the center or capital of the 
universe. 

Q. What is the Inclination of the Sun's Axis to that of 
the Ecliptic, 

A. Seven and a half degrees. 

Q. How is it known that the Sun Revolves on its Axis? 

A. By spots, seen first on the east side, which pass over 
and disappear on the west side. 

Q. What is the Xature of the Spots on the Sun ? 

A. Astronomers regard them as openings in the lumin- 
ous atmosphere, enabling us to see the opaque body of 
the sun. 



ELEMENTARY ASTRONOMY. 19 

Q. Do the Spots on the Sun always appear of the same 
size ? 

A. They do not. 

Q. What is the form of the Sun ? 

A. It is a globe, and not a flat surface, as it appears to 
the naked eye. 

Q. What is the rate of the Sun's Motion at its Equator ? 

A. Not less than 4,532 miles an hour. 

Q. What is the size and shape of the Spots on the Sun ? 

A. They are of all sizes and of different shapes. 

Q. Is the Sun Inhabited ? 

A. Nothing is known to mortals on this subject. 

Q. Will you mention some of the Advantages derived 
from the Sun ? 

A. It is the soul and center of a splendid retinue of re- 
volving worlds. 



LESSON VIII. 



Q. What are the three great Laws discovered by Kep- 
ler? 

A. 1. That all the planets perform their revolutions in 
elliptical orbits, having the sun in one of their foci. .[See 
the ellipse, A, P, B, D, on the left, near the top of the 
Chart.] C, is the center of the ellipse, and E and S, are 
the foci. 2. That the radius vector passes over equal 
areas in equal portions of time. 

Q. What is meant by the Radius Vector ? 

A. It is a line drawn from the sun to a planet in any 



20 ELEMENTARY ASTRONOMY. 

part of its orbit. In the ellipse, A, P, B, D, on the left, 
near the top of the Chart, the snn is at S, the lower foci. 
We will suppose the earth's orbit, where it is shown on 
the Chart in the twelve signs of the Zodiac, elliptical, like 
this figure (A, P, B,) a line drawn from the sun to the 
earth, where it will be on the first day of each month of 
the year, as it enters the several signs respectively, is the 
Radius Vector. 

The third law discovered by Kepler is : that the squares 
of the times of the revolutions of the planets around the 
sun, are proportional to the cubes of their mean distances 
from the sun. 



LESSON IX.— Mercury. 



Q. Where is the proper place of Mercury in the Solar 
System ? 

A. Next to the sun, as shown on the Chart. The dark 
circle surrounding the sun, represents the orbit of the 
planet, and the two small circular figures, seen at the two 
opposite points of the circle or orbit, represent the planet 
itself, as seen in its inferior and superior conjunctions, 

Q. What is the diameter of the Planet Mercury ? 

A. This planet is estimated at 32 hundred miles in 
diameter. 

Q. How far is Mercury from the Sun ? 

A. Thirty-seven millions of miles. 

Q. What is the Direction of the Planet in its Orbit 
around the Sun ? 



ELEMENTARY ASTRONOMY- 2 i 

A. From west to cast, as is indicated in the direction of 
the earth, by the months of the year in the third orbit 
from the sun, on the Chart. 

Q. What is the Rate of Motion of this Planet in its 
Orbit? 

A. One hundred and ten thousand miles per hour. 

Q. What is the Specific Gravity of the Planet Mercury ? 
A. It is about 15 times the weight of water. 

Q. How many Conjunctions has Mercury ? 

A. Two ; an inferior and a superior conjunction, 

Q. Can Mercury have an Opposition as well as his Con- 
junctions ? 

A. It cannot, because its orbit lies between the earth 
and the sun. 

Q. Do the Mean and True places of a Planet's Orbit 
ever coincide ? 

A. They do, at the aphelion and perihelion, as at A and 
B, in the ellipse, on the Chart. 

Q. What is the straight line called that passes through 
the Sun from A to B, in the Ellipse i 

A. It is called the apsis line. 

Q. Is the Planet ever behind its Mean Place \ 

A. It is ; as when it is passing from its perihelion at B, 
to its aphelion at A, in the ellipse. 

Q. When is it before its Mean Time ? 

A. When it is passing from its aphelion at A, its great- 
est distance from the sun, to its perihelion B, its least 
distance. [See the Ellipse.] 

Q. When does a Planet Move with its least Velocity I 



22 ELEMENTARY ASTRONOMY. 

A. When it is farthest from the sun, or in its aphelion, 
as at A, in the ellipse. 

Q. Why is this so ? 

A. Because the attractive influence of the sun is di- 
minished as the planet recedes from it. 

Q. When is the Motion of the Planet Increasing? 

A. When it is passing from A, its aphelion, to B, its 
perihelion, as in the ellipse. 

Q. What causes this Accelerated Motion ? 

A. The increased force of the sun's attraction on the 
planet, as it approaches nearer the sun. 

Q. What causes the Planet to Kecede from the Sun, 
from its Perihelion at B, to its Aphelion at A ? 

A. The superior centrifugal force of the planet here, 
just obtained by the sun's attraction as it advanced with 
increased velocity toward the sun. 



LESSOX X.— Mercury — Continued. 

Q. When is Mercury said to be in his Inferior Con- 
junction? 

A. When he is between us and the sun. Thus, when 
the earth is in that part of its orbit, marked in the Dia- 
gram as " September," and "Mercury" is where his name 
is red, he is in a direct line with the sun from our stand- 
point of observation. He is then between us and the sun. 
This is called his " inferior conjunction." 

Q. When is Mercury said to be in his Superior Con 1 - 
j unction? 



ELEMENTARY ASTRONOMY, 23 

A. When lie is in a direct line from our post of obser- 
vation, beyond the sun. [See the Diagram, where another 
very small circular figure is shown on the opposite side of 
the circle, in a direct line from our post of observation on 
the earth, where it is marked " September."] ' This is 
Mercury, in his superior conjunction. 

Q. Why is he shown on the Chart as appearing smaller 
in his Superior than in his Inferior Conjunction? 

A. Because he is farther from us now, by the whole 
diameter of his orbit, and hence he will appear much 
smaller than when he is nearest us, as in his inferior con- 
junction. 

Q. What is the Year of a Planet ? 

A. The time it takes to revolve around the sun. 

Q. What is the Year of Mercury ? 

A. Eighty-seven days and twenty-three hours of our 
time. But from one conjunction to the same conjunction 
again, it is about 116 days. 

Q. What is Mercury called ? 

A. An " interior planet." 

Q. Why is Mercury called an Interior Planet? 

A. Because its orbit lies within the earth's orbit, or be- 
tween the earth and the sun. The same is true of Venus. 
[See the- Diagram.] 

Q. What are all the other Planets of the Solar System 
termed? 

A. " Exterior planets ;" because they perform their re* 
volutions in orbits which lie beyond the earth's orbit. 

Q. What is the Density of Mercury ? 

A. It is about equal to that of lead. 



24 ELEMENTARY ASTRONOMY 

Q. How Swiftly does the Planet fly ? 

A. About 1,830 miles in a minute, and about 30 miles 
in a second. 

Q. What is the Light and Heat of Mercury, compared 
with that of the Earth ! 

A. It is about seven times greater. 

Q. What is the Elongation of a Planet ? 

A. The apparent distance of a planet from the sum 

Q. What is the greatest Elongation of Mercury ? 

A. Thirty degrees either west or east from the sun, 

Q. Has Mercury any Change of Seasons ? 

A. It has not. 



LESSON XL— Venus. 



Q. What Planet is next to Mercury, in the Arrange-- 
ment of the Solar System ? 

A. Venus. 

Q. What is the Diameter of Venus ? 

A. Seven thousand eight hundred miles* 

Q. How far is Venus from the Sun 1 

A. Sixty-nine millions of miles. 

Q. In what time does she Eevolve around the Siln ? 

A. Two hundred and twenty -five days- — at the rate of 
75 thousand miles an hour. 

Q. What is the Circumference of her Orbit ? 

A. Four hundred millions of miles. 

Q. What is the Specific Gravity of Venus. 

A. About five times the weight of water. 

Q. AVhat is the comparative Light and Heat of Venus? 



ELEMENTARY ASTRONOMY. 25 

A. It is about double that of the earth. 

Q. What is the greatest Elongation of Venus? 

A. About 47 degrees. 

Q. How near does the Planet ever approach to the 
Earth ? 

A. When she is in that part of her orbit nearest the 
earth, as shown in the figure, she is 27 millions of miles 
distant from us. 

Q. When is Venus the Morning Star ? 

A. When she is west of the sun, and rises before it. 

Q. When is she an Evening Star ? 

A. When she is east of the sun, and sets after it. 

Q. How long does she continue to be a Morning Star? 

A. About 270 days ; and then the same length of time 
as an evening star. 



LESSON XIL— Venus— Continued. 

Q. Why is Venus a Morning and an Evening Star, about 
66 days longer than the whole time of her Annual Revo- 
lution around the Sun ? 

A. Because, the earth is moving, though not so swiftly, 
around the sun in the same way. Venus will move 1 80 
degrees of her orbit, while the earth is moving only 110 
degrees. If the earth stood still, or kept up with Venus, 
the result would be essentially varied. 

Q. Can any other Planet approach so near the Earth as 
Venus % 

2 



26 ELEMENTARY ASTRONOMY. 

A. No. An inspection of the Diagram will show that 
no other planet of the solar system can approach so near 
the earth as this. 

Q. How much is the Axis of Venus inclined to that of 
its Orbit ? 

A. Seventy-five degrees ; so that its torrid zone will be 
150 degrees wide, or 75 on each side of its equator. 

Q. Does this Planet ever assume Different Phases, like 
the Moon ? 

A. She does. 

Q. Has Venus any Variations of Seasons? 

A. She has eight seasons — two summers and two win- 
ters at the equator; and a summer and winter at each of 
the poles during the year. 

Q. Why does Venus assume the Phases of the Moon? 

A. Because, she revolves in an orbit between the earth 
and the sun. 

Q. How many apparent Motions have the Planets 1 

A. Three ; direct, stationary and retrograde. 

Q. When is the Motion of a planet said to be direct ? 

A. When it appears to move from west to east, among 
the stars. 

Q. When is it said to be Stationary ? 

A. When it appears to be moving directly towards, or 
from the earth. 

Q. When is it Retrograde ? 

A. When it seems to move backwards, among the stars. 

Q. Is Venus attended with a Satellite or Moon ? 

A. This question is not .positively decided among as- 
tronomers. 



ELEMENTARY ASTRONOMY. 27 

LESSON XIIL— The Earth. 

Q. What is the form of the Earth ? 

A. It is that of an oblate spheriod, nearly approaching 
to that of a globe. 

Q. What is the place of the Earth in the Solar System ? 

A. The path of the earth around the sun, lies between 
the paths or orbits of Venus and Mars. [See the Chart.] 

Q. How do the Inhabitants Stand upon the Earth ? 

A. With their feet toward the center of the earth. 

Q. What keeps the Inhabitants on the Earth. 

A. The attraction of the earth. 

Q. What does the Earth rest on ? 

A. It rests on no foundation ; but it is a planetary body 
suspended in empty space, and surrounded on all sides by 
the starry heavens. 

Q. What is the Axis of the Earth? 

A. A straight line round which it performs its diurnal 
rotation; and the extremity of its axis are the poles of the 
earth. 

Q. What is the Distance of the Earth from the Sun ? 

A. About 95 millions of miles. 

Q. What, then, is the Diameter of the Earth's Orbit? 

A. Twice its distance from the sun — 190 millions of 
miles. 

Q. What is the Circumference of the Earth's Orbit ? 

A. About 600 millions of miles. 

Q. How long does it take the Earth to perform a Jour- 
ney Round the Sun ? 

A. Three hundred and sixty-five and a quarter days. 



28 ELEMENTARY ASTRONOMY. 

Q. With what Velocity must the Earth Move, to com- 
plete this revolution in this length of time ? 

A. About 68 thousand miles an hour. 

Q. What is the Equator? 

A. It is the great circle whose plane divides the earth 
into northern and southern hemispheres. This plane is 
perpendicular to the earth's axis, and is at an equal dis- 
tance from each pole. 

Q. What is the Meridian of a place on the Earth ? 

A. A great circle passing through a place, and extend- 
ing from pole to pole ; and the plane of this meridian 
divides the earth into eastern and western hemispheres. 

Q. What is the Latitude of a place on the Earth ? 

A. Its distance from the equator, north or south. 

Q. On what is Latitude measured ? 

A. On a meridian, and is reckoned 90 degrees. 

Q. What places on the Earth have 90 Degrees of Lati- 
tude ? 

A. The north and south poles. 

QUESTION ON THE CHART. 

Q. Why is every Planet, Satellite and Comet there 
shown with an Enlightened Side toward the Sun ? 
A. Because they receive their light from the sun. 



LESSON XIV. 

VARIETY OF SEASONS ON THE EARTH. 

Q. What causes the Changes of the Seasons on the 
Earth ? 



ELEMENTARY ASTRONOMY. 29 

A. The annual revolution of the earth around the sun, 
in connection with the inclination of its axis, in an angle 
of 23^ degrees from the perpendicular to the plane of 
the ecliptic. 

Q. How many Seasons have we on the Earth ? 

A. Four ; spring, summer, autumn and winter. 

Q. Can you explain from the Chart, what is meant by 
the Inclination of the Earth's Axis ? 

A, N. and S., on the Chart, where the earth is marked 
" March" and " September," will designate the north and 
south poles of the earth respectively. A straight line 
from N. to S., it is readily seen, would hot stand perpen- 
dicular, but would be inclined from the perpendicular in 
an angle of 23^ degrees. It is seen from the Diagram, 
that the axis stands thus permanently inclined through 
every month of the year, and during the entire journey 
of the earth around the sun. " This permanent inclination 
of the earth's axis from the perpendicular, and her revo- 
lution around the sun, cause first one pole to be enlight- 
ened, and then the other, thus producing the seasons. 
The same inclination and revolution, cause the sun to ap- 
pear to oscillate from north to south, crossing the equator 
twice every year." This is called the " sun's declination." 

Q. At what times of the year are the Days and Nights 
of Equal Length ? 

A. On the 21st of March and on the 23d of September. 

Q. What: causes this Equality of Day and Night at 
those times? 

A. The sun, shining equally from pole to pole. [See 

the Diagram.] 



30 ELEMENTARY ASTRONOMY. 

LESSON XV. 

Q. What is the Diameter of the Earth ? 

A. Seven thousand nine hundred and thirty miles. 

Q. How much greater is its Equatorial than its Polar 
Diameter ? 

A. About 26 miles ; and is caused by the revolution of 
the earth on its axis. 

Q. What is the Specific Gravity of the Earth ? 

A. It is about 5 \ times the weight of water. 

Q. In what Time does the Earth Revolve on its Axis, 
or complete an entire Rotation ? 

A. In 24 hours. 

Q. Which Way does the Earth Tarn on its Axis ? 

A. From west to east, as all the planets in the solar 
system do. 

Q. What results from this Rotation ? 

A. Day and night. 

Q. What portion of the Earth's Surface has Light, and 
what portion Darkness ? 

A. One half of the earth's surface is continually in the 
light of the sun, while the other half is continually in the 
dark. 

Q. Is the Earth ever Behind Time in its Rotation on 
its Axis ? 

A. No. It is uniform and exact to the second, from age 
to age. God has covenanted that there shall always be 
day and night in their seasons. 



ELEMENTARY ASTRONOMY. .°>1 

LESSON XVI.— The Seasons— Contiwxed. 

Q. When does the North Pole of the Earth, lean di- 
rectly toward the Sun ? 

A. On the 21st of June, called the " summer solstice/ 1 
[See the Diagram.] 

Q. Can you Illustrate clearly the gradual Changes of 
the Seasons from the Chart? 

A. On the 21st of March, the Diagram shows the sun 
shining equally on both poles of the earth. This is the 
reason why we have equal day and night at that time. So 
of the 23d of September, shown in the opposite side of 
the earth's orbit. But as the earth moves onward in her 
orbit, from her place in March, in the period of a month, 
she has traveled about 50 millions of miles, and her north 
polar circle is seen advancing farther into the light, and 
her south polar circle a corresponding extent into the 
dark. When the 21st of June has rolled around, and the 
earth has traveled 100 millions of miles farther in its orbit, 
the north polar circle is seen wholly in the light of the 
sun, and the south polar circle, at the same time, wholly 
in the dark. The axis of the earth is always parallel to 
itself, pointing in the same direction in the heavens. On 
the 21st of June, the sun ceases to decline from the equi- 
noctial and to return towards it. This is called the " sum- 
mer solstice." " The equinoctial points are two opposite 
sides of the earth's orbit, at which time the sun is exactly 
in the equinoctial; or in other words, the plane of the 
equinoctial cuts the sun's center," and the sun shine s 
equally from pr>le to pole. The first of the equinoctial 



32 ELEMENTARY ASTRONOMY. 

points, when, of course, the days and nights are equal, is 
reached by the earth in her flight around the sun, on the 
21st of March. 

Q. What is this called? 

A. The " vernal equinox." 

Q. When is the other Equinox, and what is it called ? 

A. The 23d of September, and is called the " autumnal 
equinox." When the earth has advanced to 90 degrees, 
or one-fourth part of her orbit, the sun ceases to decline 
from the equinoctial or equator, and begins to return to- 
ward it, as shown on the Chart, in the month of June. 

Q. How many Degrees does the North Pole of the 
Earth lean towards the Sun on the 21st of June? 

A. Twenty-three and a half degrees; and the sun is ver- 
tical 23 i degrees north of the equator. 

Q. Does this produce any Difference of Seasons from 
any other time of the year ? 

A. It produces summer in the northern hemisphere, and 
winter in the southern. An inspection of the Diagram 
will show this clearly. 

Q. When does the North Pole lean directly from the 
Sun? 

A. On the 21st of December, called the "winter sol- 
stice." [See the Diagram or Chart, where the north pole 
is turned from the sun, and is wholly in the shade, while 
the south pole is in the light.] 

Q, What are the Seasons when the North Pole leans 
from the Sun ? 

A. Winter in the northern hemisphere, and summer in 
the southern. 



ELEMENTARY ASTRONOMY. <>J 

LESSON XVIL— The Seasons— Continued. 

Q. Why are the Days the Longest, and the Nights the 
Shortest, on the 21st of June, in the Northern Hemis- 
phere ? 

A. Because the most of the northern hemisphere is 
then in the light of the sun. 

Q. Why are the Nights the Longest, and the Days the 
Shortest, at the time of the Winter Solstice, on the 21st 
of December? 

A. Because the largest part of the northern hemisphere 
is then turned from the sun, and is in the shade, 

Q. How far are the Solsticial Points from the Equinoc- 
tial Points ? 

A. Ninety degrees. All circles are divided into 360 
parts, called degrees ; and the solsticial points are respect- 
ively 90 degrees, or one-fourth part of the earth's orbit, 
from the equinoctial points. 

Q. When is the Summer Solstice Reached by the Earth 
in its Annual Journey around the Sun \ 

A. On the 21st of June, when the sun has the greatest 
northern declination, or is at its greatest distance north of 
the equinoctial, and it pours a flood of welcome light on 
all the region of the globe embraced within the north 
polar circle. The light and shade on the figure, shown on 
the Chart at this time, will show why it is summer in the 
northern hemisphere — so large a portion of this hemis- 
phere being in the light of the sun. 

Q. When i^ the Winter Solstice Reached by the Earth, 

as it flies arc md the Sun? 
2* 



34 ELEMENTARY ASTRONOMY. 

A. On the 21st of December, when the sun is at its 
greatest distance south of the equinoctial ; or in other 
words, has the greatest southern declination, as in the 
figure, and it is summer in the southern hemisphere, and 
winter in the northern. [See the Earth, in the Diagram, 
in June and December.] 

Q. How far does the Sun Decline to the North and 
South of the Equinoctial ? 

A. About 23^ degrees, answering to the inclination of 
the earth's axis from the perpendicular, by which it is 
caused, and marking the limits of the tropics upon the 
earth's surface. 

Q. How 7 long have the North and South Poles of the 
Earth the Light of the Sun, respectively ? 

A. The north pole of the earth has the light of the 
sun, from the vernal equinox, on the 21st of March, to the 
autumnal equinox, on the 23d of September ; and then 
the south pole advances into the light, which it continues 
to enjoy until the 21st of March. 

Q. Is this an Equal Division of the Year, giving to each 
Pole the Light of the Sun just one-half of the time? 

A. No. The north pole has the light of the sun about 
eight days longer than the south pole. 

Q. How is this produced? 

A. The orbit of the earth is elliptical, and the earth has 
to pass through 180 degrees of its orbit, which occupies 
186 days 11 hours ; but while the earth is passing through 
the other part of its orbit, from the 23d of September to 
the 21st of March, it passes through only 11 6 degrees, 
which is performed in 178 days 18 hours. As the earth 



E L E M E NT A R V AST ltONOM V. 



moves in an elliptical orbit, it is farther from the sun in 
the northern than in the southern hemisphere, and as a 
result, moves slower. 



LESSON XVIII.— The Seasons— Continued, 

Q. What causes the North Pole to have the Light of 
the Sun for six months, and then to be deprived of the 
light the balance of the year? 

A. The earth's revolution round the sun. The Diagram 
shows the sun shining on the north pole for six months, 
and the south pole deprived of his light for the same 
length of time. From March 21st to September 23d, the 
sun shines without intermission on the north pole, and 
during this time the south pole is in the dark.' At these 
points, it is equal day and night, because both poles are 
equally enlightened by the sun. But from March to June, 
the larger portion of the northern hemisphere is in the 
light of the sun, and the rotation of the earth on its axis 
gives us a longer day than night. As the poles of the 
earth always point in the same directions in the heavens, 
it will be seen by the Diagram that it is the earth's revo- 
lution around the sun that brings first one pole of the earth 
into the light of the sun for six months, and then in turn 
the other. 

Q. Why are not the Days and Nights of Equal Length 
at all times of the year ? 

A. It is owing to the inclination of the earth's axis, in 
connection with its revolution around the sun, that we 



30 ELEMENTARY ASTRONOMY. 

have a difference in the length of day and night, at differ- 
ent periods of the year. The light and shade shown on 
the earth from March 21st to June 21st, in the Diagram, 
presents a giadual increase of enlightened surface on the 
northern hemisphere. 

Q. Does the Diagram show the Light and Shade exact- 
ly as they are on the Earth at all times ? 

A. The liorht and shade on the earth daring the several 
months of the year, in the Diagram, are not designed to 
exhibit the exact quantity of light and shade on any par- 
ticular portion of the earth ; but rather the proportions of 
light and shade on the two hemispheres. The figure 
shows, that while one pole of the earth is in the dark, 
being deprived of the light of the sun, the other pole is, 
to a corresponding extent, in the light. But while exhibit- 
ing these facts, it is impracticable to have, on a plane sur- 
face like the Diagram, all the enlightened parts of the 
earth appear as turned toward the sun, and all its unen- 
lightened parts appear as turned from it. 

Q. What is the Length of Day and of Night at the 
Poles ? 

A. Six months. 



LESSON XIX.— The Zodiac. 

Q. What is the Zodiac ? 

A. By the "zodiac," is meant an imaginary belt, 16 
degrees wide, viz: 8 degrees on each side of the ecliptic, 
and extending from west to east, quite round the heavens. 



ELEMENTARY ASTRONOMY. 37 

Q. What is meant by the Signs of the Zodiac? 
A. Certain clusters of stars, situated in twelve different 
parts of that great circle of the heavens through which 
the sun appears to move, and through which the earth 
actually does move, in its annual journeys. 

Q. Who Invented the Constellations forming the Zo- 
diac ? 

A. It was probably the work of the Egyptians and 
Chaldeans. 

Q. How is the Zodiac Divided? 

A. Into 12 equal parts, called " constellations," or the 
" signs of the Zodiac ;" and each sign is divided into 30 
degrees ; each degree into 60 minutes ; each minute into 
60 seconds, &c. 

Q. Where is the Ecliptic or Orbit of the Earth ? 
A. It is in the middle of the Zodiac. 
Q. Will you give the Names of the Constellations of 
the Zodiac ? 

A. Aries, (or the Ram,) Libra, (the Balance,) 
Taurus, (the Bull,) Scorpia, (the Scorpion,) 
Gemini, (the Twins,) Sagittarius, (the Archer,) 
Cancer, (the Crab,) Capricornus, (the Goat,) 
Leo, (the Lion,) Aquarius, (the Waterman,) 

Virgo, (the Virgin,) Pisces, (the Fishes.) 

Q. What is the Order of the Signs around the Heavens 
A. Beginning at Aries, eastward, around to Pisces. 
Q. Are the Constellations of the Zodiac and the Signs 
of the Ecliptic in the same place in the Heavens ? 

A. Thev were about 2,200 years ago ; but the signs of 



38 ELEMENTARY ASTRONOMY. 

the ecliptic have fallen back of the constellations about 31 
degrees, caused by the retrograde motion of the equinoxes. 

Q. Upon what does the Length of the Seasons Depend ? 

A. The revolution of the earth from one equinox to 
the same equinox again. 

Q. Does the Earth Move from one Equinox to the 
' same again, in exactly the time it Revolves around the 
Sun? 

A. It requires 17 minutes longer to revolve around the 
sun. 

Q. Does the Sun revolve aro'ind the Heavens ? 

A. The sun has only an apparent, and not a real, 
motion among the stars, from east to west, caused by the 
actual motion of the earth from west to east. 

Q. Where is the Real Place of the Earth in March ? 

A. In Libra, and consequently the sun will appear in 
the opposite sign, Aries, and be vertical to the equator, as 
shown in the figure of the earth at that place. 

Q, Where is the Earth in June I 

A. In Capricorn ; and the sun is in the opposite sign, 
Cancer, when he is vertical to those who live under the 
tropic of Cancer. 

Q. Where is the Place of the Earth in September? 

A. In Aries, and the sun is in the opposite sign, Libra, 
when lie is again vertical to the equator, 

Q. Where is the Earth in December? 

A. In Cancer, and the sun in Capricorn, when he is 
vertical to those living under the tropic of Capricorn, as 
the inhabitants of the southern parts of Africa and the 
central parts of New Holland. 



E L E M E XT A R Y AST 110 N M Y. 

Q. What are the Spring Signs of the Ecliptic ? 

A. Aries, Taurus, Gemini. 

Q. What are the Summer Signs? 

A. Cancer, Leo, Virgo. 

Q. Which are the Autumnal Signs? 

A. Libra, Scorpio, Sagittarius. 

Q. Which are the Winter Signs? 

A. Capricornius, Aquarius, Pisces. 



LESSON XX.— Mars. 



Q. What is the Place of Mars in the Solar System ? 

A. Mars is the fourth planet from the sun. 

Q. What is the Size of Mars? 

A. It is the smallest in the solar system, except Mercu- 
ry and the Asteroids. It is 4,200 miles in diameter. 

Q. What is the Periodic Time of Mars ? 

A. Six hundred and eighty-seven days, or one year and 
322 days of our time. 

Q. What is the Distance of Mars from the Sun ? 

A. One hundred and fourty-five millions of miles. 

Q. What is the Specific Gravity of this Planet? 

A. About five times the weight of water. 

Q. How many Degrees does the Axis of Mars Lean to- 
wards its Orbit? 

A. About 30 degrees. 

Q. Has this Planet any Change of Seasons ? 

A. It has. Its seasons will vary but little from ours, as 



40 ELEMENTARY ASTRONOMY. 

its axis are inclined only 6|- degrees more than those of 
the earth's. 

Q. What is the Length of its Day and Night ? 

A. About the same as ours. The day of Mars differs 
but 44 minutes from the day of our globe. 

Q. What way does it Revolve in its Diurnal and Annual 
Revolutions ? 

A. From west to east. 

Q. What is the Length of the Seasons of Mars ? 

A. About twice the length of ours. 

Q. What is the Appearance of Mars when seen through 
a Telescope ? 

A. A red fiery color. 

Q. What amount of Light and Heat has Mars ? 

A. About half as much as the earth. 

Q. Does the Bright Appearance about its Poles con- 
tinue during the Whole of its Year? 

A. It disappears during the summer. 

Q. What does the Striking Resemblance between this 
Planet and the Earth Indicate ? 

A. That the design of the Creator was not essentially 
different in its formation from that of the earth. It has 
all the arrangements essentially requisite to its being a 
habitable world. 



LESSON XXL— Mars— Continued. 

Q. Is Mars an Interior or Exterior Planet ? 

A. Mars is an exterior planet, because it performs its 



ELEMENTARY ASTRONOMY. 41 

annual journies around the sun in an orbit lying- exterior 
to the orbit of the earth. 

Q. How many Conjunctions have the Interior Planets? 

A. Two. [See Mercury and Venus, in the Diagram, 
and Lesson X.] 

Q. How many Conjunctions have the Exterior Planets ? 

A. One conjunction and one opposition. 

Q. When is Mars in his Conjunction? 

A. When he is beyond the earth, in the same part of 
the heavens as the sun. 

Q. When is he in Opposition ? 

A. When the earth is between him and the sun. This 
will readily be understood by the Diagram. When the 
earth is at the place in her orbit, designated as " Septem- 
ber," and Mars is at the place in his orbit where his name 
is red, he is then said to be in his " opposition ;" and 
when he is seen on the opposite side of his orbit, he is 
then said to be in his " conjunction," because he is then 
in the same part of the heavens as the sun. The small cir- 
cular figure seen at that point, is Mars, in his conjunction. 

Q. Why does he Appear so much Smaller on the Op- 
posite Side of his Orbit? 

A. At distances so essentially different, it will necessa- 
rily result that his apparent magnitude will not always be 
uniform. 

Q. How Far is Mars from the Earth when at his 
Greatest Distance ? 

A. Two hundred and forty millions of miles. 

Q. How Near to the Earth does this Planet ever Ap- 
proach ? 



42 ELEMENTARY ASTRONOMY. 

A. Fifty millions of miles. When nearest the earth, lie 
is nearer by the whole diameter of the earth's orbit, or 
190 millions of miles. This will appear by an inspection 
of the Diagram at this point. 



LESSON XXII.— The Asteroids. 

Q. What are the Asteroids ? 

A. They are small planets ; and all perform their revo- 
lutions between the orbits of Mars and Jupiter — a space 
of about 349 millions of miles. 

Q. How Many Asteroids are there ? 

A. Fifty-seven, so far as now known. 

Q. What is the Magnitude of the Asteroids ? 

A. They are all small, probably less than our moon. 

Q. Do they all Revolve in Orbits Similar to the other 
Planets ? 

A. Some of their orbits are more eccentric, and the 
orbit of Pallas crosses the orbits of other planets. 

Q. What are the Names of the Asteroids, and the Date 
of their Discovery ? 

A. 

No. Name. Date of Discovery. No. Name. Date of Discovery, 

1. Ceres, 9. Metis. 1847, Oct. IS. 

2. Pallas, 1801, Jan. i. 10. Hydea. 1848, Apr. 25. 

3. Juno, 1802, Mar. 28. 11. Porthenope, 1849. Apr. 12. 

4. Testa, 1804. Sept. 1. 12. Clio 1850. May 13. 

5. Astaea, . . . . .1807, Mar. 20. 13. Egeria. 1850, Sept. 13. 

6. Hebe, 1845, Dec. 8. 14. Irene, 1850, Nov. 2. 

7. Iris, 1847. July 1. 15. Eunomia, .. 1851, May 20. 

8. Flora. 1847. Au.o-.13. 16. Psyche. ... .1851, July 29. 



ELEMENTARY ASTRONOMY. 



I:; 



No. Name. Date of Discovery, 

17. Thetis, 1852, Mar. 17. 

18. Melpomene, 1852, Apr. 17. 

19. Fortuna, 1852, June 24. 

20. Massilia, ...1852, Aug. 22. 

21. Lutetia, 1852, Sept. 19. 

22. Calliope, 1852, Nov. 15. 

23. Thalia, 1852, Nov. 16. 

24. Themis, 1852, Dec. 15. 

25. Procea, 1353, Apr. 5. 

26. Proserpina,.. 1853, Apr. 6. 

27. Euterpa, 1853, May 5. 

28. Bellona, 1853, Nov. 8. 

29. Amphitrite, 1854, Mar. 1. 

30. Urania, 1854, Jnly 22. 

31. Euphrosine. 1854, Sept. 1. 

32. Pomona, . . ..1854, Oct. 26. 

33. Polyhymnia, 1854, Oct. 28. 

34. Circe, 1855, Apr. 15. 

35. Leucothea, ..1855, Apr. 19. 

36. Atalanta, ...1855, Oct. 5. 



No. Name. Date of Discovery. 

38. Leda, 1856, Jan. 12. 

39. Lastetia, 1856, Feb. 8. 

40. Harmonia, . .1856, Mar. 31. 

41. Daphne, 1856, May 23. 

42. Isis, 1856, May 25. 

43. Ariadne, . . . .1857, Apr. 15. 

44. Nysa, 1857, May 27. 

45. 1857, June 27. 

46. Hestia, 1857, Aug. 16. 

47. Aglaia, 1857, Sept. 16. 

48. Doris, 1857, Sept. 19. 

49. Pales 1857, Sept. 19. 

50. "Virginia, . . .1857, Oct. 4. 

51. Nemansa, ..1858, Jan. 22. 

52. Europa, 1858, Feb. 4. 

53. Calypso, 1858, April 4. 

54. Alexandria, 1858, Sept. 11. 

55. Pandora, ...1858, Sept. 11. 

56. Melete, 

57. Mnemosyne, 



37. Fides, 1856, Oct. 5. 

Q. In what Length of Time do the first four of these 
Planets Revolve around the Sun ? 

A. Vesta, in one thousand three hundred and thirty-one 
days. 

Q. What is the Periodic Time of Juno ? 

A. One thousand five hundred and ninety-three days. * 

Q. What is the Periodic Time of Ceres ? 

A. One thousand six hundred and eighty-one days. 

Q. What is the Periodic Time of Pallas? 

A. One thousand six hundred and eighty-seven days. 

Q. Are any of the Asteroids or Small Planets attended 
with Satellites? 



44 ELEMENTARY ASTRONOMY. 

A. This question is not positively decided among as- 
tronomers. 



LESSON XXIIL— Jupiter. 

Q. What is the Name of the next Planet beyond the 
Asteriods ? 

A. In the arrangement of the solar system, Jnpiter is 
placed next in order beyond the asteroids. His orbit lies 
between the asteroids and that of Saturn. 

Q. How Large is Jupiter ? 

A. Jupiter is the largest planet in the solar system yet 
discovered, being nearly 89 thousand miles in diameter, 
making it over 14 hundred times as large as the earth. 

Q. How Far is Jupiter from the Sun ? 

A. Four hundred and ninety-five millions of miles. 

Q. How Near does this Planet ever Approach to the 
Earth ? 

A. When nearest the earth, Jupiter is about 400 mil- 
lions of miles from us. 

Q. How Far is he Ever from the Earth ? 

A. When farthest off, he is 590 millions of miles dis- 
tant, being, as will be seen by the figure, farther by the 
whole diameter of the earth's orbit, which is 190 millions 
of miles. 

Q. Which Diameter of this Planet is the Greatest, the 
Polar or the Equatorial ? 

A. The equatorial diameter is 6,000 miles greater than 
the polar, which results from the very rapid rotation of 
the planet on its axis. 



ELEMENTARY ASTRONOMY. 45 

Q. In what Time does it Revolve on its Axis ? 

A. In about ten hours and a half. 

Q. What is the Velocity of its Equatorial Parts in 
Turning on its Axis? 

A. Twenty-eight thousand miles an hour — 3,000 miles 
more than the equatorial parts of the earth's surface move 
in 24 hours. 

Q. How Many Days are there in the Year of Jupiter? 

A. Ten thousand four hundred and seventy. 

Q. What Amount of Light and Heat has this Planet? 

A. It has about 27 times less light than the earth. 

Q. Will there be any considerable Difference in the 
Length of the Days and Nights of Jupiter? 

A. There will be nearly equal day and night in every 
part of the surface of this planet ; but the sun will rise to 
a high elevation above its horizon to places near the equa- 
tor. 

Q. How Many Moons has Jupiter? 

A. Jupiter is attended by four moons. In the Diagram 
they are shown in their orbits at different distances from 
the planet. 

Q. What is the Direction of the Moons of Jupiter ? 

A. They all move from west to east, according to the 
order of the signs, as do all the planets of the system. 

Q. From What Source do they Derive their Light ? 

A. From the sun. 

Q. How does Jupiter Appear when Viewed with a 
Telescope? 

A. The disc of Jupiter is streaked with curious belts, 
running parallel to his equator. 



46 ELEMENTARY ASTRONOMY. 

Q. Who first Discovered the Moons of Jupiter ? 

A. Galileo, the inventor of the telescope, in 1610. 

Q. What is their Magnitude ? 

A. The magnitude of these satellites differ but little 
from that of oar moon. The third one, however, is some- 
what larger. 

Q. How are the Orbits of the Moons of Jupiter Situ- 
ated ? 

A. They are directly over his equator. 

Q. What are the Periodic Times of their Revolutions? 

A. They perform their revolutions in periods of from 
one day 18 J- hours, to 16 days 16 hours, according to 
their distances. 



LESSON XXIV.— Jupiter— Continued. 

Q. What are the Magnitudes and Distances of Jupiter's 
Moons ? 

A. Their magnitudes and distances are as follows ? 

DIAMETER IN MILES. 

First, 2,500. Third, 3,777. 

Second, 2,068. Fourth, 2,890. 

DISTANCE FROM THE PRIMARY I 

From 260,000.... to 1,180,000. 

Q. Do the Moons of Jupiter ever Suffer Eclipses? 

A. The planet is shown in the Diagram as casting a 
shadow in the direction opposite to the sun. Its moons 
or satellites, in revolving around it, will frequently fall 
into its shadow, and will suffer numerous eclipses. The 



ELEMENTARY ASTRONOMY. 4-7 

satellites of Jupiter pass through this broad shadow, when 
in opposition to the sun, and are totally eclipsed at every 
revolution. The fourth satellite, however, sometimes 
passes above, and sometimes below, and thus escapes 
being eclipsed. These moons often eclipse Jupiter, by 
throwing their dark shadows upon his disc, as is seen on 
the Chart, in the case of the fourth moon. About forty 
of these eclipses occur in the system of Jupiter every 
month. 

Q. What great Discovery was Made by Observing the 
Eclipses of Jupiter's Moons ? 

A. It was by observations upon the eclipses of Jupiter's 
moons, as compared with the tables fixing the time of 
their occurrence, that it was discovered that light had a 
progressive motion of about 192 thousand miles per 
second. 

Q. Will you Illustrate this from the Chart? 

A. The orbits of Jupiter and the Earth are concentric, 
and hence the mutual distances of these globes will be 
continually varying. Direct your attention to Jupiter, 
with his system of moons, and to the Earth in its orbit 
around the sun. It is evident that when the Earth is in 
that part of its orbit designated as " December," it will 
be the whole diameter of its orbit, which is 190 millions 
of miles farther from Jupiter than when he is at the place 
in his orbit, marked as "June." If light were instanta- 
neous, the satellite now seen immersed in Jupiter's shadow, 
would appear to enter into this shadow, to a spectator on 
the earth, when it is farthest distant from Jupiter, as in 
" December," at the same moment as to another spectator, 



48 ELEMENTARY ASTRONOMY. 

when the earth is nearest, as in M June;" but from numer- 
ous observations, it was found that when the earth was at 
its greatest distance from the planet, the immersion of the 
satellite into the shadow of the planet, happened 16 min- 
utes and 22 seconds later than when the earth was nearest, 
as in " June." 

Q. What Conclusions were drawn from this? 

A. It was therefore concluded that light was not in- 
stantaneous, but requires a certain space of time to fly 
from one part of the universe to another, and that the 
time it takes in passing from the sun to the earth, or across 
the semi-diameter of the earth's orbit, is 8 minutes and 13 
seconds, giving it a motion of 192 thousand miles per 
second — a motion of more than 10 thousand that of a 
cannon ball when first projected from the cannon's mouth. 

Q. What is the Density of Jupiter \ 

A. About \\ that of the earth. 

Q. How was the Rotation of the Planet and the Length 
of its Day Determined ? 

A. By watching spots in the belts of the planet. 



LESSON XXV.— Saturn. 



Q. What is the Next Planet in the Solar System beyond 
the Orbit of Jupiter ? 

A. Saturn, at the distance of 907 millions of miles 
from the sun, and about 412 millions of miles beyond the 
orbit of Jupiter. 

Q. What is the Size of the Planet Saturn ? 



ELEMENTARY ASTR0K0MY. 49 

A, He is about 79 thousand miles in diameter, andt 
about 1,000 times larger than the earth. 

Q. What is the Specific Gravity of Saturn ? 

A. About the same as that of cork, or about one-half 
the weight of water. 

Q. In what Time does this Planet Revolve on its Axis ? 

A. Ten hours and 16 minutes. 

Q. How Many Days will this Planet have in its Year? 

A. Twenty-five thousand one hundred and fifty. 

Q. What is its Motion on its Axis at the Equator ? 

A. It is about 24 thousand miles an nour — 2,000 miles 
greater than its rate of motion in its annual revolution 
around the sun. 

Q. Is there any Change of Seasons at Saturn ? 

A. There is, but the change comes very slow, as it re- 
quires nearly thirty of our years to complete a year at 
Saturn. 

Q. How Long does it take this Planet to Perform a 
sideral Revolution Around the Sun ? 

A. Twenty-nine and a half years. 

Q. What is the Circumference of his Orbit ? 

A. A distance of about 5,700 millions of miles. 

Q. What surrounds Saturn ? 

A. Saturn is encircled by two magnificent rings. 

Q. What is the Position of these Rings in Reference to J 
the Planet? 

A. They are directly over its equator. 



50 ELEMENTARY ASTRONOMY. 

LESSON XXVL— Saturn— Continued. 
QUESTIONS ON THE CHART. 

Q. How and Where is Saturn Shown in the Diagram ? 

A. Saturn, with his suite of rings, is shown in perspect- 
ive in its orbit, " S." near the lower side of the Chart ; 
but he is more accurately exhibited, with his rings and 
moons on the opposite side of his orbit, near the top of 
the figure. 
* Q. How are the Rings Shown there? 

A. In a circular form. Our view of the planet is gen- 
erally an oblique one, and hence these rings never appear 
circular, but usually elliptical. If either pole of the planet 
were exactly towards us, we should have a perpendicular 
view of the rings. 

Q. What are the Dimensions of these Eings, in round 
numbers ? 

Miles. 

A. Distance from the planet to the first ring, 19,000. 

Width of the interior ring, 17,000. 

Space between the interior and exterior rings, 2,000. 

Width of the exterior ring, 10,000. 

Thickness of the rings, 100. 

Exterior diameter of exterior ring, .176,418. 

Interior diameter of exterior ring, 155,272. 

Exterior diameter of interior ring, 151,690. 

Interior diameter of interior ring, 117,339. 

Q. What Good Purpose do these Rings Answer to the 
Planet? 

A. They serve as reflectors to throw the light of the 
sun upon the planet, as our moon does upon the earth. 



ELEMENTARY ASTRONOMY. 51 

Q. How Many Satellites or Moons has Saturn ? 

A. Eight. 

Q. Do they Revolve with the Planet and Rings ? 

A. These moons and rings all revolve with the planet. 

Q. What is the Position of the Orbits of Saturn's 
Moons ? 

A. All of them, excepting one, are directly over the 
rings. 

Q. What is the Form of the Orbits of Saturn's Moons ? 

A. The moons of Saturn revolve in orbits nearly cir- 
cular. 

Q. How Near are these Moons to the Planet ? 

A. Their mean distances from the planet, are from 
123,000 to 2,366,000 miles. 

Q. In how long a Time do they perform their Revolu- 
tions around the Planet ? 

A. They perform their sideral revolutions around their 
primary, in periods of from 22£ hours to 79 days, accord- 
ing to their distances. 

Q. Do the Satellites of Saturn ever Suffer Eclipses ? 

A. They are seldom eclipsed. Yet they may be on 
rare occasions, as shown in the Diagram, in the case of 
the third from the planet. 

Q. What will Result from the Small Density and Rapid 
Rotation of the Planet on its Axis ? 

A. It will materially diminish its otherwise attractive 
force, and contribute, in accordance with the great law of 
gravitation, to retain the rings and moons in the places 
assigned them in the system of Saturn. 



52 ELEMENTARY ASTRONOMY, 

LESSON XXVII. 

URANUS. 

Q. When, and by Whom, was Uranus Discovered ? 
A. In 1781, by Sir William Herschel, a celebrated Eng- 
lish astronomer. 

Q. What is the Distance of this Planet from the Sun ? 
A. Its distance, in round numbers, is 1,850 millions of 
miles. 

Q. What is the Diameter of Uranus ? 

A. About 35 thousand miles, making it about 8 times 
as large as the earth. 

Q. What is its' Specific Gravity ? 

A. It is 1-J- times the weight of water. 

Q. In What Part of the Solar System is Uranus situ- 
ated? 

A. Uranus is the seventh large planet from the sun, and 
revolves in an orbit lying between Saturn and Neptune. 

Q. What is its Eate of Motion in its Orbit ? 

A. Fifteen thousand miles an hour. 

Q. In How Long a Time does it Revolve Around the 
Sun? 

A. Eighty-four years. 

Q. What Place in the Solar System was Uranus Sup- 
posed to hold at the Time of its Discovery ? 

A. At the time of its discovery, it was situated at the 
extreme limits of the solar system, so far as was then 
known. 

Q. What Appendages has Uranus attending it? 

A. Uranus is attended With six moons. 



ELEMENTARY ASTRONOMY. 53 

Q. In what Direction do these Moons Move in their 
Orbits? 

A. They revolve in an order contrary to the analogy of 
the whole solar system. Their orbits are nearly perpen- 
dicular to the ecliptic, advancing from east to west, while 
the other planets, with their satellites, move from west to 
east. 

Q. Are these Satellites ever Eclipsed ? 

A. Proceeding from east to west, the second satellite, 
as shown in the Diagram, occasionally falls into the shadow 
of the planet, and suffers an eclipse. Yet eclipses are not 
of frequent occurrence in the system of Uranus. 

Q. What are the Distances and Periodic Times of these 
Moons ? 

A. Their distance and periodic times are as follows : 

Distance in Miles from the Primary. Periodic Times. 

1st, 240,000 5 days 21 hours. 

2d, 296,000 8 " 11 " 

3d, 340,000 10 " 23 " 

4th, 390,000 13 " 11 " 

5th, 777,000 38 " 2 " 

6th, 1,555,000 117 " 17 " 

Q. What is the Eccentricitv of the Orbit of Uranus? 

A. About 85 millions of miles. 

Q. When was the Planet Neptune Discovered ? 

A. In 1846. 

NEPTUNE. 

Q. By Whom was Neptune Discovered ? 

A. By a French astronomer, Leverier, and also by a Mr. 
Adams, of Cambridge, England, who has put in his claim 
as the discoverer. 



54 ELEMENTARY ASTRONOMY. 

Q. What is the Place of this Planet in the Solar 
System ? 

A. So far as now known, it is placed at the extreme 
limits of the solar system. 

Q. What is its Distance from the Sun ? 

A. Two thousand eight hundred and fifty millions of 
miles. 

Q. What is its Diameter ? 

A. About the same as that of Uranus — 35,000 miles. 

Q. What is its Magnitude ? 

A. It is about 81 times as large as the earth. 

Q. In what Time does it Eevolve Around the Sun ? 

A. In about 164 years of our time. 

Q. What is its Rate of Motion per Hour ? 

A. About 11,000 miles. 

Q. Has it any Rings or Moons Attending it? 

A. This planet is known to be attended by at least one 
satellite. 



LESSON XXVIII.— The Moon. 

Q. What is the Moon ? 

A. It is a secondary planet, revolving around the earth. 

Q. Why is the Moon Called "a Secondary Planet?" 

A. Because, it revolves around another planet, called 
a "primary planet." The primary planets revolve around 
the sun as their center of motion, while the secondary 
planets or moons, revolve around their primaries as their 
center of motion, and accompany them in their long jour- 
neys around the sun. 



ELEMENTARY ASTRONOMY. 55 

Q. What was the Design of God in Creating the Se- 
condary Planets or Moons ? 

A. This design is apparent from the inspired statement 
of the purposes for which our moon was created. It is as 
follows : " And God said let there be lights in the firma- 
ment of heaven, to divide the day from the night ; and let 
them be for signs and for seasons ; and for days and for 
years; and let them be for lights in the firmament, to give 
light upon the earth ; and it was so. And God made two 
great lights ; the greater light to rule the day, and the 
lesser light to rule the night. And he made the stars also." 
Gen. 1, 14—16. 

Q. How Many Moons have the Different Planets ? 

A. The Earth has one; Jupiter, four; Saturn, eight; 
Uranus, six ; and Neptune, one ; making twenty in all, so 
far as is positively known. 

Q. Is the Moon Larger or Smaller than the Earth ? 

A. It is 49 times smaller. 

Q. What is the Diameter of the Moon ? 

A. Two thousand one hundred and sixty miles. 

Q. What is its Mean Distance from the Earth ? 

A. Two hundred and forty thousand miles. 

Q. How Long does the Moon Require to make a Com- 
plete Revolution Around the Heavens 2 

A. Twenty-nine and a half days. 

Q. What is this Revolution Through the Heavens 
called ? 

A. It is called the " moon's synodic revolution." 

Q. In how Long a Time does the Moon Make a Revolu- 
tion Around the Earth from one Fixed Star to the same 
Star again ? 



56 ELEMENTARY ASTRONOMY* 

A. Twenty-seven days, 7 hours and 43 minutes? 

Q. What is this Revolution Called ? 

A. It is called her u tropical or periodic revolution." 

Q. What is the Cause of this Difference of about two 
Days between the Snyodic and Periodic or Tropical Revo- 
lution of the Moon? 

A. This difference of time results from the onward mo- 
tion of the earth in its orbit around the sun at the same 
time that the moon is performing her revolution around 
the earth. At new moon, the sun and moon are in the 
same part of the heavens ; but by the time the moon has 
returned to that point, namely, 27 days, 7 hours, 43 min- 
utes, the earth has proceeded in its orbit around the sun, 
27 degrees farther to the east, and is still going on, and 
the moon has to undertake it before she can be again m 
that position which is called " new moon." [See th@ 
Diagram.] 

Q. Does the Moon always Accompany the Earth ! 

A. The moon is the constant attendant of the earth 
from age to age, in all its long journey round the sun. 

Q. Which Way does the Moon Revolve Around the 
Earth? 

A. From west to east, as all of the bodies of the solar 
system do, except the satellites of Uranus. 

Q. Why, then, Does the Moon Rise in the East? 

A. Because^ the earth revolves from west to east, 



ELEMENTARY ASTRONOMY. 57 

LESSON XXIX,— The Moon— Continued. 
QUESTIONS ON THE CHART. 

Q. How is the Moon Shown in the Diagram ? 

A. The moon is there shown in eight different posi- 
tions, which it assumes in its orbit around the earth. 

Q. What Are the Eight Different Positions? 

A. ik New moon," when she is directly between the 
earth and the sun ; the "slender crescent," as she is seen 
on about the third da} 7 after the change ; " half moon," 
as seen on the eighth day after the change; "gibbous 
phase," when more than one-half of her enlightened disc 
is turned to the earth ; and after a few days more, her 
whole enlightened hemisphere is turned towards the earth, 
and she appears a "fall moony 

Q. How does She Appear After This ? 

A. She decreases, turning every day less and less of 
her enlightened hemisphere to the earth, exhibiting, in 
turn, the " gibbous phase," " half moon," " crescent," and 
then the "new moon," when she is in conjunction as be- 
fore, and her dark side is turned to the earth, and she is 
invisible. 

Q. In How Long a Time does She Pass Through these 
Changes ? 

A. In 29 days, 12 hours and 44 minutes, at an average, 
which is termed her " synodical revolution." 

Q. Why does the Moon Show only a Crescent in Cer- 
tain Points of her Orbit \ 

A. Because, her enlightened side is turned to the sun, 

and from our stand point on the earth, we can see only a 

small part of that enlightened surface. 
3* 



58 ELEMENTARY ASTRONOMY. 

Q. Why is She next Shown as a Half Moon ? 

A. Because, as she has advanced in her orbit, a larger 
portion of her enlightened hemisphere is turned towards 
the earth. 

Q. Why does She Appear as Full when in Opposition 
to the bun ? 

A. Because, in that part of her orbit, her whole enlight- 
ened hemisphere is turned to our view. 

Q, How does She Appear After This? 

A. Her enlightened disc gradually diminishes, exhibit- 
ing, in turn, a "gibbous face," " semi-circle," and " cres- 
cent," until she is finally lost sight of for a short time 
during the period of " new moon." 

Q. Does the Moon Eise the Same Hour every Evening ? 

A. She rises about 50 minutes later every evening. 

Q. Why does She Eise Later every Evening? 

A. Because, she revolves round the earth from west to 
east, 

Q. If the Moon Stood Still, would She Exhibit the 
Phases Shown in the Diagram \ 

A. She would not. 

Q. When is it " New Moon ?" 

A. When the moon is between the earth and the sun, 
and her dark side is towards the earth and she is invisible. 

Q. When is it " Full Moon }" 

A. When the moon is upon the opposite side of the 
earth from the sun, and her enlightened side is turned to- 
wards the earth. [See Diagram.] 

Q. What is the Appearance of the Moon when Viewed 
with a Telescope ? 



ELEMENTARY ASTRONOMY. 59 

A. Its appearance is interesting and variegated. It 
seems like a map or model of another world, resembling 
in its prominent features, the earth. It is diversified with 
vales and mountains, and is covered with light and dark 
spots of various shapes. 

Q. Has the Moon any Oceans, Seas or Large Bodies of 
Water! 

A. This question has long engaged the attention of 
astronomers, without being settled. It is not clear that 
there are any large bodies of water on the side towards 
the earth, though it is not improbable that small lakes or 
rivers exist there. As we can see only one side of the 
moon, of course we know nothing of its opposite hemis- 
phere. 

Q. If you were Living on the Hemisphere of the Moon, 
towards the Earth, How would the Earth Appear ? 

A. Like a brilliant moon over our heads, suspended in 
empty space, stationary, and about 13 times larger than 
does the moon to us. 

Q. What is the " Harvest Moon ?" 

A. It is the full moon in September and October, when 
it rises only a few minutes later for a number of successive 
evenings, and thus affords light for collecting the harvest. 



LESSOR XXX.— The Moon— Continued. 

Q. Which is the Largest, the Moon or the Sun ? 
A. The sun is about 70 millions of times larger than 
the moon. 



60 ELEMENTARY ASTRONOMT. 

Q. Then Why do they Appear to be About the Same 
Size? 

A. Because, the sun is 400 times farther from us than 
the moon. The sun is 95 millions of miles distant from 
us, while the moon is but about 240 thousand miles dis- 
tant. 

Q. When the Moon is in the Point of Her Orbit Near- 
est the Earth, where is She said to be ? 

A. In " perigee." 

Q. When She is in the Point of Her Orbit Most Dis- 
tant from the Earth, where is She said to be ? 

A. She is said to be in " apogee." 

Q. What are these Two Opposite Sides of Her Orbit 
Called? 

H. "The apsides of her orbit," and a line joining them 
is called/' the line of the apsides" 

Q. Does the Moon Move in a Circular Orbit ? 

A. The orbits of all the planets, both primary and 
secondary, are more or less elliptical. 

Q. When She Seems to Run Over and Obscure the Dis- 
tant Planets and Stars, in Her Journey around the Earth, 
wMbt is this Called \ 

A. This is called an " occulation." 

Q. AVhat is the Moon's Orbital Velocity, with respect 
to the Earth ? 

A. About 2,300 miles an hour. 

Q. But, as She keeps up with the Earth Around the 
Sun, at the Same Time, What is Her Rate of Motion ? 
A. Not less than 70,300 miles an hour. 



ELEMENTARY ASTRONOMY. L 

Q. What are the Extreme Points of the Crescent 
Shown in the Figure of the Moon, Called ? 

A. They are called the " cusps of the moon." 

Q. What are the Two Points in Her Orbit Called, where 
She is Shown in the Diagram, as " New " and " Full 
Moon," 90 Degrees apart? 

A. They are called her "syzigies." 

Q. What are the Quadrations of the Moon ? 

A. They are four points in her orbit, 90 degrees apart, 
or a quarter of the circle of her orbit. 

Q. What are Her "Octants?" 

A. They are eight points in her orbit, as the eight 
places in the cut, where is shown in the Diagram. 

Q. When the Moon Comes in Conjunction with the 
Sun, and is changed from "Old Moon" to'"Xew Moon," 
what is She said to do? 

A. She is said to " change" 

Q. What is the Rocking or Rolling of the Moon in 
Her Orbit, Called ? 

A. It is called her " libration in longitude." 

Q. What is the Rate of the Moon's Motion on its Axis, 
from West to East ? 

A. Only about 10 miles an hour. 

Q When is the Velocity of the, Moon in Her Orbit 
Greatest ? 

A. When she approaches the periods of " new" and 
" full moon." 

Q. Has the Moon a Rotation on its Axis ? 

A. She has. She 'revolves on her axis in about 2 To- 
days, or just the time in which she revolves around the 
earth. 



62 ELEMENTARY ASTRONOMY. 

Q. Do we Ever See More than One Hemisphere of the 
Moon ? 

A. We do not. 

Q. Why do we Not See the Other Side of the Moon ? 

A. Because, she revolves on her axis in the same length 
of time that she revolves around the earth, which neces- 
sarily always keeps the same side towards us. 

Q. Is there Any Difference Between the Length of a 
Lunar Day, Month and Year ? 

A. The length of time is the same; about 29-J- days. 

Q. What is a Lunation or Lunar Month ? 

A. It is the time from one new moon to another. 

Q. What Motion has the Moon ? 

A. The moon must have a compound motion, since it 
revolves both around the sun and around its primary. 

Q. To What Laws is the Moon Subject ? 

A. It is subject to the same law of gravitation, and of 
centripetal and centrifugal forces, as that of its primary, 
the earth. 

Q. What Kind Office does it Afford the Earth ? 

A. It serves as a mirror, to reflect the light of the sun 
on the earth. 

Q. W^hat is the Eccentricity of its Orbit? 

A. Thirteen thousand three hundred and thirty-three 
miles. 



KLEMENTAtlY ASTRONOMY. 63 

LESSON XXXI. —Eclipses. 

Q. What is an Eclipse \ 

A. An eclipse is a privation of the light of the sun, or 
of some other heavenly body, by the interposition of an- 
other body between it and our sight. 

Q. How are Eclipses Divided, with respect to the body 
eclipsed ? 

A. Into solar and lunar. Eclipses are either of the sun 
or the moon, or of the satellites which accompany some 
of the planets. 

Q. How are Eclipses Divided, in respect to circum- 
stances ? 

A. They are divided into total, partial, annular, and 
central. 

Q. What is a Total Eclipse ? 

A. When the whole face of the luminary is darkened,, 

Q. What is a Partial Eclipse ! 

A. When only a part of the disc is darkened. 

Q. W r hat is an Annular Eclipse? 

A. It is when the whole is darkened except a rino; or 
annualis, which appears round the dark part, like an illu- 
minated border. 

Q. What is a Solar Eclipse? 

A. An eclipse of the sun. 

Q. What Causes a Solar Eclipse ? 

A. The interposition of the body of the moon between 
the sun and the earth, when she throws a shadow over a 
certain portion of the earth. 

Q, When Must an Eclipse of the Sun Take Place? 



64 ELEMENTARY ASTRONOMY. 

A. It can only happen at the time of the " new moon/' 
and when the moon is at or near one of her nodes. 

Q. Will you illustrate the Nature of a Solar Eclipse by 
the Diagram ? 

A. A solar eclipse is shown in the Diagram where the 
earth is represented in the month of July. The dark 
circle around the earth there represents the orbit of the 
moon ; the circular figure in the circle, is the moon ; and 
the cone or w r edge extending to the earth, is the moon's 
shadow. The moon is in that part of its orbit next the 
sun, having its enlightened side towards the sun, and its 
dark side towards the earth, which is its position at "new 
moon." It is in its node, in an exact line between the sun 
and the earth. Here the shadow of the moon naturally 
falls upon a certain portion of the earth, and intercepts 
the rays of the sun for a little time from those portions of 
the earth on whom the shadow falls. * 

Q. Do we Have an Eclipse of the Sun at Every New 
Moon ? 

A. We do not ; because at " new moon," the shadow 
generally falls above or below the earth. 

Q. Why does the Moon's Shadow take the form of a 
Cone, as shown in the Figure ? 

A. Because, the moon is smaller than the sun. 

Q. Does this Shadow Ever Come to a Point before 
Reaching the Earth ? 

A. It sometimes happens that the extremity of the cone 
of the moon's shadow falls short of the earth. 

Q. What Will this Produce? 

A. An annual eclipse of the sun ; in which case the 



ELEMENTARY ASTRONOMY. 65 

sun appears like a brilliant ring of light around the dark 
body of the moon. 

Q. What is the Length of the Moon's Shadow? 

A. Two hundred and thirty-four thousand miles — 6,000 
miles less than the mean distance of the moon from the 
earth, and hence it will frequently fail to reach the earth, 



LESSOX XXXII.— Eclipses— Continued. 

Q. Why Are Not all Eclipses of the Sun Total ? 

A. Because, the moon, being so small, compared with 
the sun, and being so far from the earth, its shadow, in 
accordance with the laws of shadows, terminates in a point 
before it reaches the earth. In order to a total eclipse, 
the moon must be in its perigee or nearest to the earth. 

Q. How Long May a Total Eclipse of the Sun Continue 
at any one Place on the Earth ? 

A. Xot over four minutes. 

Q. How is an Eclipse of the Moon Produced? 

A. By an interposition of the earth between the sun 
and the moon. 

Q. When Can an Eclipse of the Moon Take Place? 

A. Only at " full moon," when the moon is in opposi- 
tion to the sun. [See the Diagram, where the earth is 
shown in the month of January.] 

Q. W r hy Does the Earth Cast a shadow, as there shown, 
in a Direction Opposite to the Sun ? 

A. Because she is an opaque body, and enlightened by 
the sun. 



66 ELEMENTARY ASTRONOMY. 

Q. How Far will this Cone or Shadow of the Earth 
Reach before Terminating in a Point ? 

A. About 840 thousand miles. 

Q. Why Does Not the Moon Suffer a Total Eclipse at 
the Time of Every Full Moon ? 

A. Because, she does not always move in the plane of 
the ecliptic, so as to pass through the center of the earth's 
shadow. 

Q. How Many Eclipses may Take Place in a Year ? 

A. Seven ; five of the sun and two of the moon. Two 
is the smallest number that can happen, and both must be 
of the sun. 

Q. Why are there More Eclipses of the Sun than of the 
Moon ? 

A. Because the solar ecliptic limit is far greater than 
that of the moon. 

Q. What is a " Digit ? " 

A. It is the twelfth part of the apparent diameter of 
the sun or moon's disc. 

Q. Are Visible Eclipses of the Moon More Frequent, 
at any Particular Place, than those of the Sun ? 

A. They are. 

Q, Why are they ? 

A. Because, an eclipse of the moon is visible, and ap- 
pears as great to all places on the earth where the moon 
is above the horizon. 

Q. Where does an Eclipse of the Moon Begin ? 

A. An eclipse of the moon always begins on the moon's 
eastern side, and goes off on her western side. 

Q. How Far are Eclipses of the Moon Visible ? 



ELEMENTARY ASTRONOMY. 67 

A. In all parts of the world, where the moon is above 
the horizon ; and are everywhere of the same magnitude 
and duration. 

Q. How is the Moon's Diameter Divided ? 

A. It is supposed to be divided into twelve equal parts, 
called " digits," and as many of these parts as are darken- 
ed by the earth's shadow, so many digits is the moon said 
to be eclipsed. 

Q. Is the Moon Invisible when Totally Eclipsed ? 

A. She is not, if she is above the horizon, and the 
atmosphere is clear. 

Q. How does the Moon Appear when Eclipsed ? 

A. Generally of a dusky color, somewhat like tarnished 
copper, especially towards the edges, being generally more 
dark about the middle of the earth's shadow. 

Q. Is the Moon Always Visible During a Lunar 
Eclipse f 

A. It is not. 

Q. What is Meant by the "Umbra" of the Moon, 
Earth, or any of the Planets ? 

A. It is the total dark shadow of the planet. 

Q. What is the " Penumbra ?" 

A. It is a faint shadow surrounding the umbra. 

Q. What is the Greatest Extent of the Moon's Umbra 
upon the Earth ? 

A. One hundred and seventy-five miles. 



68 ELEMENTARY ASTRONOMY. 

LESSON XXXIIL— Eclipses— Continued, 

Q. Where do Eclipses of the Sun Begin ? 

A. They always begin on its western side. It will be 
seen from the Chart, in the Diagram of a solar eclipse, 
that the eclipses of the sun necessarily come from the 
tvest, and pass over eastward. The reason of this is very 
obvious, since the moon passes from west to east, between 
the earth and sun. 

Q. Why do Eclipses of the Moon Begin on her East- 
ern Side ? 

A. Because, the moon passes from west to east, through 
the earth's shadow. 

Q. In what Direction does the Moon's Shadow Pass 
Over the Earth in a Solar Eclipse ? 

A. As shown in the Diagram, it passes over the earth 
from west to east. 

Q. What is the Duration of a Central Eclipse of the 
Moon, when the Moon is at her Greatest Distance from 
the Earth ? 

A. Three hours, fifty-seven minutes, twenty-six seconds, 
from beginning to end. 

Q. What is the Duration of a Central Eclipse of the 
Moon, when She is at her Least Distance from the Earth ? 

A. Three hours, thirty-seven minutes, twenty-six seconds. 

Q. Can the Moon be Totally Eclipsed Without Passing 
Through the Center of the Earth's Shadow ? 

A. She can. 

Q. How Large a Portion of the Earth's Surface may 
be Covered by the Moon's Penumbra ? 



ELEMENTARY ASTRONOMY. 69 

A. A space of about 4,393 miles in diameter. 

Q. Will you Explain from the Diagram, the Philosophy 
of a Lunar Eclipse ? 

A. The nature and cause of eclipses will readily be 
understood by an inspection of the Chart. A lunar 
eclipse is there shown, in connection with the earth, when 
at the place in her orbit designated as " January." The 
earth is there shown as casting a shadow from it in the 
form of a cone. All the planets, both primaries and 
secondaries, cast shadows in a direction opposite to the 
sun. The sun being larger than the earth, the shadow will 
take the form of a cone, as shown in the figure, and will 
end at a point at the distance of about 840,000 miles from 
the earth. The dark circular figure seen there, in the 
earth's shadow, and in the circle surrounding the earth, 
represents the moon ; and the circle itself, the orbit of the 
moon. The moon is then in opposition to the sun, and is 
passing through the earth's shadow. As the earth is 
about 8,000 miles in diameter, its shadow near its surface, 
must be about 8,000 miles broad. But as the shadow of 
the earth takes the form of a cone, and as the moon is 
about 240,000 miles from the earth, the earth's shadow at 
that distance, will be about 6,000 miles broad ; and, as the 
moon is only 2,160 miles in diameter, she must be com- 
pletely immersed in the shadow of the earth, and must 
move nearly three times her whole diameter before she 
can emerge from the shadow. 

Q. Are Eclipses Matters of any Considerable Import- 
ance to Mankind ? 

A. Eclipses constitute some of the most grand and sub- 
lime phenomena of the heavens, 



70 ELEMENTARY ASTRONOMY. 

LESSON XXXIV.— Comets. 

Q. What other Bodies, Besides the Sun, Planets and 
their Satellites, Belong to the Solar System ? 

A. Another singular class, called " cornets." The course 
of comets will be better understood by turning your atten- 
tion to the right hand on the Chart, where one is shown 
as flying across the orbits of the planets, and advancing 
near the sun, and then departing. 

Q. How do these Singular Bodies Appear? 

A. They gradually come into view, increasing in bright- 
ness and velocity until they attain a maximum, where they 
remain for a time, then as gradually diminish, pass off, and 
are lost in the distance. 

Q. Are Comets Solid Bodies, Like the Planets? 

A. Our knowledge of these bodies is very limited, and 
no decisive opinions of them can safely be pretended. 

Q. What is the Meaning of the Word " Comet?" 

A. This word literally signifies a hairy star, because 
comets are generally accompanied with a nebulous ap- 
pearance or train, which has the resemblance of lumin- 
ous hair. 

Q. What is the Nucleus of a Comet ? 

A. The luminous point near the center, which is the 
most brilliant. 

Q. What is the Hair or Envelope of a Comet? 

A. The haze or nebulosity which surrounds the nucleus* 

Q. What is called the Tail of a Comet? 

A. The luminous train, which sometimes extends to a 
great distance from the head, is the tail of the comet. 



ELEMENTARY ASTRONOMY. 71 

Q. Was the Existence of Comets Known to the 
Ancients ? 

A. It was. Comets have occasionally appeared in the 
heavens in all ages. 

Q. What is the Direction of the Luminous Tail of 
Comets ? 

A. Usually on the opposite side from the sun ; but a 
few have been observed to have a different direction. 

Q. Wliat are Comets now Supposed to be ? 

A. Since the days of Sir Isaac Newton, they have been 
considered as bodies constituting parts of the solar system, 
and that their motions are performed in long eclipses, hav- 
ing the sun in one of their foci. 

Q. Do Comets Always Appear Attended with the Ap- 
pendage of a Luminous Train ? 

A. Some have appeared without such an appendage. 

Q. Do Comets all, like the Planets, Revolve in the Same 
Direction Round the Sun ? 

A. They do not. They come plunging from all points, 
down into the solar system, and pass round the sun, and 
then take their departure in greatly elongated orbits, as 
shown in the Diagram. 

Q. Are the Orbits of all the Comets Within the Limits 
of the Zodiac ? 

A. They are not. They are in all parts of the heavens. 

Q. "What is the Appearance of the Comet, as it Re- 
cedes from the Sun ? 

A. It is a remarkable fact, that the real diameter of its 
nebulosity increases proportionally as the comet becomes 
distant from the sun. This remarkable circumstance has 



72 ELEMENTARY ASTRONOMY. 

been attempted to be accounted for, but no satisfactory 
hypothesis has yet been reached. 

Q. What is the Form of the Orbits of Comets? 

A. They are extremely eccentric* and form very el on* 
gated ellipses. 

Q. What is the Periodic Time of Comets ? 

A. Many Comets are supposed to have periods of a 
thousand years. 

Q. To what Distance do they Go from the Sun ? 

A. It must be very great, since they are absent so long 
from our system. 



LESSON XXXV. 



I have now given a brief description of all the planets* 
satellites and comets of the solar system, with the sun as 
the central and controlling force, that retains them in 
their orbits from age to age. 

The harmony, order, simplicity and wisdom, displayed 
in the structure of the solar system, will be better appre- 
ciated by a minute inspection of the Chart, where the 
planets are all seen in their proper places, attended by 
their respective moons, and all revolving with great rapid- 
ity in their orbits — the primaries around the sun, and the 
secondaries around their respective primaries. Meantime 
all are in swift rotation on their axis, thus turning their 
different sides alternately to and from the sun, and secur- 
ing the indispensably important and agreeable vicissitudes 
of day and night, and change of seasons, proportioned to 



ELEMENTARY ASTRONOMY. t -• 

the inclination M' their axis. The sun is seen as placed 
in the center, which is the most feasible point from which 
to send out incessant streams of light and heat to all this 
vast family of distant and revolving worlds. 

GRAVITATION. 

Q. What is " Gravitation C 

A. It is the act of tending to the center, or of being 
drawn towards something — the tendency of all matter in 
the universe towards all other matter. Every portion or 
body of matter attracts and is attracted, directly as its 
quantity of matter, and inversely, as the square of its dis- 
tance from the attracting body. 

Q. Is this the Binding Force that Holds all the Heav- 
enly Bodies in their Appropriate Places? 

A. It is. 

Q. Will you more Fully Illustrate and Explain the Prin- 
ciples of Gravitation ? 

A. When one body revolves around another as its 
center of motion, it is influenced by two forces : one of 
which tends to make it fly off from the central body, and 
the other to approach it. 

Q. What are these two Principles Called that thus Ope- 
rate upon the Flying Body ? 

A. They are called " centrifugal" and " centripetal" 
forces. 

Q. What is the Nature of the Centrifugal Force? 

A. It tends to make a body fly off from the central 
body. 

Q. What is the Centripetal Force? 
4 



ELEMENTARY ASTRONOMY. 

A. It is that force or principle that impels the flying- 
body to approach the central body. 

Q. Will you Illustrate the Practical Operations of these 
two Opposite and Contending Principles' or Forces? 

A. When a boy fastens a stone to one end of a string, 
and holding the other in his hand, whirls the stone around, 
it describes a path or orbit under the action or influence 
of centrifugal and centripetal forces. 

Q. Suppose that while the stone is in rapid motion,, the 
string should be suddenly cut, would it continue, to re- 
volve in a circle ? 

A. It would not. It would quickly fly away from the 
hand, the center of its orbit. 

Q. What Force or Principle Makes it Fly Off? 

A. Its centrifugal force. When the string was whole 
the stone was prevented from obeying the centrifugal 
force, and was kept in a circular path by the resistance of 
the centripetal force — the string in the boy's hand, which 
actually drew it towards the center of its orbit, with a 
power that just balanced the centrifugal force that would 
drive it off in a straight line. The power of the string is 
therefore the centripetal force. 

Q. In the light of these definitions and this illustration, 
can you not More Fully Illustrate the Principle of Attrac- 
tion ? 

A. We will suppose that a power of attraction resides 
in the boy's hand, which draws the stone towards him, 
instead of a material bond, as a string, just as a magnet 
draws to itself any particles of iron that may be near it. 
This is the principle on which the power of attraction 



E LE M E N T A 11 V A ST R( )NUMV. ib 

works. The attractive power (centripetal force,) is so 
nicely adjusted to the centripetal force or the force that 
drives off the stone in a straight line, when free, that one 
force just counterbalances the other, and. the stone is made 
to describe a circular path. 

Q. Is this the Principle on which the Planets and Satel- 
lites are made to Revolve in their Orbits around the Sun ? 

A. It is. A heavenly body revolves about the central 
orb under the action of centrifugal and centripetal forces ; 
but it is not bound to its central orb by any material bond, 
as a cord or chain. There actually resides in the central 
body, an attracting force, which constitutes the centripetal 
power, and balances the centrifugal force, or tendency to 
fly off. 



LESSON XXXVL— Gravitation— Continued 

Can you give any other Example of the Operations 
of the Force of Gravity ? 

A. When an apple falls from a tree, it descends in a 
straight line towards the center of the earth, under the in- 
fluence of what is termed the force of gravity. There 
must, therefore, reside in the earth a power which tends 
to draw the apple towards its center. This power is the 
centripetal force illustrated more fully in another lesson. 

Q. Can you give another Illustration of the Workings 
of the Forces Described. 

A. When a cannon ball is fired into the air, it does not 
continue its course in a straight line, as it would if influ- 



i tf E L K M E N T A K Y A S T R N OMT. 

enced only by a projectile force; but it describes a curved 
line under the influence of the force of gravity, and is 
finally drawn to the earth. 

Q. On what Circumstance will the Extent of Surface 
passed over by the Projected Body, depend ? 

A. On the greatness of the projectile force; and if the 
projectile force be sufficiently great, it is reasonable to sup- 
pose that the projected body might be carried completely 
round the earth to the point whence it started. And 
should the projectile force remain the same, with no abate- 
ment, the projected body would continue its circuit from 
a^e to a^e, like the moon. 

Q. Does this law of Gravitation Pervade all Matter? 

A. This is a universal law, extending to all matter in 
the universe. It is this law of gravitation that retains all 
the planets in their orbits. The Omnipotent and All-wise 
God has made the sun of such determinate size, and placed 
it at just the proper distance from the planets, and so 
nicely adjusted their density and motions to this great 
central and controlling force, that when the planets are 
once launched into space, the centrifugal force with which 
they are thrown forward in a straight course, is happily 
counterbalanced by the centripetal force — the sun's at- 
traction — that it is drawn into a curved line, and made to 
describe the circle, delineated on the Diagram, as the 
form of a planetary orbit. 



fi L E M E NT V R V A ST RO N M Y . 1 7 

LESSON XXXVII. 

HOW TO FIND THE CIRCUMFERENCE OF THE EARTH. 

Q. How is it Known that the Diameter of the Earth is 
about 8,000 miles, and its Circumference 25,000? 

A. It is determined as follows : " All circles, great or 
small, are supposed to be divided into 360 equal parts, 
called degrees. From this it is seen that a degree has no 
definite measure ; but depends upon the magnitude of the 
circle. If we suppose a circle to be 360 miles in circum- 
ference, then one degree would measure just one mile ; 
but if the circle were greater, a degree would be greater, 
and if less, a degree would be less. We will now apply 
this principle of the circle to measure the circumference 
of the earth. In order to do this, we must take two 
places some distance apart, and under the same meridian ; 
for example, New York and Albany. We will suppose 
that the distance between the two places has been found, 
by exact measurement, to be 138-g- miles. (This distance, 
probably, does not vary much from the truth.) We will 
now place an observer at each point, with accurate instru- 
ments, and on a particular night, at 12 o'clock, the observ- 
er at New York finds a particular star exactly in his zenith, 
or over his head ; but the observer at Albany finds the 
same star two degrees to the south of his zenith. Hence, 
it will be seen that there are two degrees between the 
two places ; and as the distance, by measurement, was 
found to be 13 8-5- miles, the two degrees between New 
York and Albany, are equal to 138£ miles, or one degree 
equals 69^ miles. Now, if we multiply the number of 



ELEMENTARY ASTRONOMY. 



degrees in the whole circumference of the earth, (3(50) by 
69^ miles, it will give 24,930 miles as the whole circum- 
ference of the earth." — Smith's Illustrated Astronomy. 



LESSON XXXVIII. 



HOW TO FIND THE DISTANCES OF THE PLANETS 
KEOM THE SUN. 

Q. How can the Distance of a Planet from the Sun be 
Found? 

A. By one of the three great laws discovered by the 
celebrated astronomer, Kepler, viz: All the. planets are 
subject to one general law, which is, that the "squares of 
their periodic times are proportional to the cubes of their 
mean distances from the sun." 

Q. Do Astronomers Recognize the Validity of this law? 

A. They do. This law was more fully unfolded and 
demonstrated by Sir Isaac Newton. 

Q. How did Astronomers find the Periodic Times of 
the Planets ? 

A. By observing the time it took each planet to revolve 
around the sun from any particular star to the same star 
again. 

Q. Did Astronomers Find it as Easy to Determine the 
Distance of a Planet from the Sun, as they did its Pe- 
riodic Time ? 

A. They did not. They found the task very difficult. 

Q. How was the Distance of the Earth from the Sun 
Found? 



ELEMENTARY ASTRONOMY. i \) 

A. It was found by observations made upon the transits 
of Venus. Calculations based upon this data, determined 
the distance of the earth from the sun, to be about 95 
millions of miles. 

Q. But How Can the Distance of the Planets be De- 
termined from any such Circumstances? 

A. As we have the periodic times of the planets, and 
have the distance of one of them from the sun, by this 
law of Kepler's, we can find the distance of the other 
planets by the simple rule of proportion. 

Q. Will you Make an Application of this Rule, in De- 
termining the Distance of Mercury from the Sun ? 

A. To do this, w T e say, as the square of 365 days (which 
is 133,225,) is to the cube of 95,000,000 of miles (which 
is 857,375,000,000,000,000,000,000,) so is the square of 
_ 88 days (which is 7,744) to a fourth term, which is the 
cube of Mercury's distance from the sun. And when the 
cube root of this term is extracted, the answer is found to 
be 37,000,000 of miles, nearly. 



LESSON XXXIX. 

HOW TO FIXD THE MAGNITUDES OF THE PLANETS. 
Q. By what Rule do Astronomers Determine the Mag- 
nitude of the Planets? 

A. It has been found that the magnitudes of all globes 
or spheres, are in proportion to one another, as the cubes 
of their diameters. Hence, if we cube the diameters of 
any two globes, and divide the greater product by the less, 
the quotient will show how many times the one is greater 
than the other. 



80 ELEMENTARY ASTRONOMY, 

Q. What is the Cube of any Number? 
A» It is the number multiplied into itself, and that pro- 
duct multiplied by the first number. 

Q. Will you Give an Example of the Cube, (fee. ? 

A. Take two globes, one of five feet, and the other ten 

feet in diameter : 

5 10 

5 10 

25 100 

5 10 



125 cube of 5. 1000 cube of 10. 

Then 125-^-1000) 
8 1000 C 

Hence it is manifest that the globe of ten feet in diame- 
ter is eight times the magnitude of a globe five feet in 
diameter. 

Q. How Large would the Sun appear if Shown in its 
Relative Magnitude to the Planets ? 

A. It would more than fill up all the space on the Chart 
within the orbit of Jupiter. 

Q> Where are the Comparative Distances of the Planets 
Shown? 

A. At the lower side of the Chart, the scale is shown 
between the orbits of Uranus and Neptune. The perpen- 
dicular lines indicate the respective distances of the plan- 
ets from the sun and from each other. S, designates the 
sun; M, Mercury; V, Venus; E, the Earth; A, the 
Asteroids; J, Jupiter: • S, Saturn; U, Uranus; and N, 
Neptune. 



TESTIMONIALS OF COMMENDATION 

TO 

E II M N S ' C II A RT OF THE SOLAR S Y S T E M , 



State of New York, ) 

Superintendent's Office, Dep't Public Instruction, > 

Albany, January 30, 1860. ) 

William Emmons, Esq. — Dear Sir: I regard your Chart of the 
Solar System, as admirably adapted to enlist the attention of Schol- 
ars, and to impart an accurate knowledge of the relative position 
and movements of the heavenly bodies. I trust you may be suc- 
cessful in securing its introduction into the Schools, where it. must 
prove a useful auxiliary in promoting Astronomical Studies. 
I have the honof to remain. 

Your obedient servant. 

H. H. TAN DYCKE. 

Sup't Pub. Instruction, 



State of Pennsylvania, ) 

Department of Common Schools, ' V 

Harrisburg, Jan. 28, 1864. ) 

Mr. William Emmons — Dear Sir : I have examined as carefully 
as my limited time would allow, the Chart of the Solar System pre- 
pared by yourself. It appears to be accurate, and it presents the 
whole subject to the eye at one view, in so compact a form, that it 
can but be instructive and interesting to those who desire to gain 
a knowledge of the position, size, orbits, velocities, and the various 
phenomena of the bodies that compose our system. I recommend 
its introduction to the directors of the several Schools in this Com- 
mon wealth, 

a 11. COBURN. 



§2 TESTIMONIALS. 

We entirely concur with others in commending " Emmons' Chart," 
as a valuable piece of Apparatus for Schools and Families. 

DANIEL READ, 
E. S. CARR, 

University of Wisconsin. 



I fully agree with Professors Read and Carr, of the State Univer- 
sity of Wisconsin, in their commendation of " Emmons' Astronomi- 
cal Chart," and believe it worthy of general patronage. 

DANIEL DRAKE, 

State Sup't of Public Instruction. 



Oberlin, Ohio, Nov., 1860. 

Dear Sir — I have examined " Emmons' Astronomical Chart." I 
have no hesitation in recommending its general introduction into 
the Schools of our country. It will do* much to give the young a 
correct impression of the Solar System, and will afford invaluable- 
aid to the Teacher. 

Yours truly,. 

C. H. CHURCHILL, 

Prof, of Math. & Nat, Philos. & Teacher of Astronomy, 

Oberlin College. 



Genesee College, Lima, N. Y. 

I have examined the Chart of Mr. Emmons, and would commend 
it to Teachers, as a valuable aid in teaching Astronomy. 

JOHN MORRISON REED, 

President of G-enesee College. 

We concur in the above. WM. HOPKINS, 

WM. WELLS, 
E. E. E. BRAGDON, 

Profs, in Genesee College. 



TESTIMONIALS. 83 

Mr. Wm. EMMONS — Sir : I have examined your Chart of the So- 
lar System. * * * * I cheerfully recommend it as worthy of 
a place and attention in every school. 

VICTOR M. RICE, 

Late Supt. of Pub. Inst, State of New York. 



State of Indiana, ) 

Department of Public Instruction, [- 

Office of the Superintendent, Feb. 11, 1861. ) 

Mr. William Emmoxs — Dear Sir: I am glad to learn that you 
are making an effort to introduce into the Schools of the State, 
your Chart of the Solar System, as an article of School furniture. 
The effect cf its instruction will be, to furnish the children at an 
early age, a pretty good idea of the shape, proportion and move- 
ments of the Astronomical Bodies. It will also induce in children 
a taste for the study of the Science of Astronomy, which they will 
be likely to pursue, more or less, in a more mature life. I advise 
all Township Trustees and School Teachers of Towns and Cities, to 
add it to their list of School furniture as soon as the means of their 

doing so will justify. 

With much respect, 

Your obedient servant, 

SAMUEL L. HUGG, 
Superintendent of Public Instruction.. 



LIBRARY OF CONGRESS 



ill 



$D JOB 0-JgWO 801 j> 



WM. S. FALLS, 

Over 21 Buffalo Street, 

ROCHESTER, N.Y. 

In returning thanks to his friends and the public, for their 

very liberal patronage, would respectfully solicit 

a continuance of their favors. 

WITH NEW TYPE AND OTHER MATERIAL, 

HE It CABLED TO EXECUTE 

PLAIN & MGY JOS PRINTING 

IN A SUPERIOR MANNER. 

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Bank Checks, Circulars, Law Work, 

Bill t .eads. Catalogues, Handbills, 

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Ball Cards, Nursery Work, Labels, &c. 

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PATRONAGE RESPECTFULLY SOLICITED. 



